SS SL TERRELL ie RE RAR TIC ; ar. ee at ere ae ee eR pr eS ese et e Ey - Par] ° 3 * = a oT De as ey ee a ee t z ‘ © Raymond Pettibon RESEARCH LIBRARY fee ty RESEARCH INSTITUTE JOHN MOORE ANDREAS COLOR CHEMISTRY LIBRARY FOUNDATION q bays _~ ee we . he sy) Ae ee ‘PIT “0D & spawmpy “yayovys *sassayy Aq patjddns syur mod{ payursg aye[q-F wor pasiejua ‘saqe][q peziisuas Ayyetoads uo ‘C-r/4A GZ Ja£ouNTeq Joyesuaduio7) 9UO pUR “1OJPa}]ayyJ 9UO ‘eIBUUeT) ainsodxy-9uQ) YUM JOyINY 94} Aq udye | NOLHOIGH LV AWILYHWWNS ‘4 i f Byepaths of Colour Photography laser 1h ARIE: Edited and with an Introduction by Weel AM «GAMBLE PO S:, 5 Wakes. NEW YORK: Peer TON & COMPANY 681 FIFTH AVENUE Made and Printed in G ae ta HUMPHRIES & CO., LT a CONTENTS. AUTHOR’S PREFACE THE EDITOR’S INTRODUCTION ; THE DAWN OF THE ONE-EXPOSURE GAMERS THE EARLY ONE-EXPOSURE CAMERA THE CHROMOSCOPE REAL INVENTIONS REFRACTION PRISM SEPARATION EXCENTRIC PROJECTION DOUBLE REFLECTIONS INCORRECT REFLECTIONS CURVED SURFACES SOME COMPENSATIONS : BENNETTO’S SYSTEM AND COMPENSATION COMPARATIVES AND ANOMALISM IN REFLECTOR CAMERAS ADDITIVE AND SUBTRACTIVE LIGHT PROJECTION CoLouR ENIGMAS ADDITIVE versus SUBTRACTIVE FILTER ARRANGEMENT LIGHT FILTERS : THEORETICAL MAKING OF LIGHT FILTERS a PLATES FoR ONE-EXPOSURE CAMERAS .. = CoLourR SENSITIZING oe a ni ie CORRECT COLOUR REPRODUCTION a e x BALANCING OF FILTERS AND PLATES .. EXPOSURE LABORATORY Ay CAMERA CONSTRUCTION VERIFYING THE Focus PROCESS FAKING DIAPOSITIVES THE GREY PRINTING PLATE LANTERN SLIDES IN COLOUR BLUE TONING CARBON PRINTING CARBON TRANSFER CINEMATOGRAPY IN COLOURS KINO-STEREOSCOPY a, se . ' “a = Pe . + a 2 | F ike ~ ] ; : . + ; : . i Vf * AUTHOR’S PREFACE AUTHOR’S PREFACE, HOTOGRAPHY in colours has now been taken up as a Be in of leading interest. In this new sphere the one-ex- posure camera is, or has been, declared a desideratum. It was first suggested by Ducos du Hauron in December, 1874, but scored its first practical victory not with the subtractive method, or method as applied to printing, but with a viewing instrument for the additive method of colour photography, called by the maker the Chromoscope. I hope in the subsequent pages of this book to show how certain defects of the early inventions can be removed and a simplified instrument developed, so that the corrected One-exposure Camera may ultimately be a useful one in the hands of the subtractive colour- worker. In a general way it is only for the subtractive method that I have compiled these notes, which are based on my own practical experience, and I have refrained from using the “ additive”? method of inserting ‘‘ cuttings ” from other sources as my own ideas. Before I give a description of my own system, I think it but right to throw sidelights on some fallacies which have prevented, and still prevent, the use of the additive Chromoscope as an instru- ment for the substractive method of colour photography, so enabling others to avoid them, and also to enable them to form their own opinions on the different systems. All things considered, it must be an advantage all round to know these fallacies for technical reasons, as well as from the historical point of view. COLOUR PHOTOGRAPHY The various chapters were written at different times and were intended for separate publication, hence certain repetitions, which, on deciding to issue in book form, I may not have eliminated. When I offered my manuscript to Messrs. Penrose, Mr. W. Gamble agreed at once to undertake the supervision of the thoughts I had laboriously put to paper. I am, however, not sure in my mind who should be more obliged to him for this self-imposed task, the reader or myself. I find that he has not substantially altered the matter nor revised it so as to hide my independence. If the reader or critic finds something or other to find fault with in what I have written, it must unreservedly be put to my account. I have a lin- gering hope that some portion of my work, in this special branch of photography, will be of use, and that such acknowledgment will also be a recompense to my mentor. O. REG. Vi. THE EDITOR’S INTRODUCTION THE EDITOR’S INTRODUCTION. devoted many years of his life to the study of colour photo- graphy, but having been mainly engaged in assisting others to work out colour problems he has not obtained the credit of pub-. licity for his ideas, which include numerous ingenious forms of colour cameras displaying considerable ingenuity of thought. He has not confined himself to putting his ideas on paper, but has con- structed many intricate models of colour cameras with his own hands and has tested them thoroughly. The opinions he expresses in this book may, therefore, be relied upon as practical. That he has not been able to carry out his inventions in a commercial way, owing either to lack of opportunity or means, should not detract from their value. ‘Lew author of this work is a practical photographer who has When the manuscript of the present book was submitted for consideration with the view to publication, it was seen to contain a good deal of information on methods of colour photography which would prove extremely useful to those who are working in this field, or to those who might contemplate taking up the study of the subject. The danger which besets experimenters in colour photography is that they may be unconsciously led, through lack of knowledge of what has been done before, into bye-paths which have already been well trodden by previous experimenters and proved to lead in no useful direction. This book will certainly prevent that, if carefully perused, and will indicate some of the best ways of procedure, be- sides furnishing such material for thought as may guide the would- be inventor of colour cameras or colour processes towards some valuable discovery. There is still a wide field for research in colour photography, as, although the principle has been established, many problems remain yet unsolved. Perhaps the one fault that may be found with the book, is that it does not cover the whole range of the subject, nor does it go into the underlying theories of colour work. But the author has specialized in a certain branch of the subject where he thought there was the Vil. COLOUR PHOTOGRAPHY greatest promise of success; he has dealt only with the methods he has himself worked and is thoroughly cognisant of, and this makes the book all the more valuable. It will, perhaps, be helpful to the reader if in this introduction we outline the history and the development of the three-colour theory, indicating some of the methods which have gone beyond the experimental stage and have been brought more or less into use. Disregarding the efforts made by scientists, even before the invention of photography, to fix the colours of the spectrum on chemically-prepared surfaces we must give credit to Louis Ducos Du Hauron, a Frenchman, for the invention of three-colour photo- graphy as we now generally understand it. His work dates from 1859 when he foreshadowed this process in a paper read before a French scientific society. This was followed by fuller publication of his idea in 1862 when the photographic reconstitution of colours was clearly defined. In 1869 Du Hauron published the first hand- book of photography in colours, in which he described all essentials for success with the process. One of Du Hauron’s suggestions was to place three sensitive surfaces one behind the other like the leaves of a book and make one exposure through them in an ordinary camera. He predicted that this method, which he calls the dialytic system, would in the end supersede all three-colour systems. It should be noted, therefore, that it is upon a modification of that method the author of the present work pins his faith as the process most likely to give successful results. Mr. F. E. Ives, a most prolific inventor of three-colour cameras and methods, seems to have arrived at a similar conclusion, for his latest method appears to be based on the same idea. Whilst we give credit to Du Hauron for the earliest publication of the three-colour idea it is but fair in the interests of historical ac- curacy to also mention the work of James Clerk Maxwell, who had apparently been working on the problem without knowledge of Du Hauron’s efforts. Lecturing at the Royal Institution in 1860, Maxwell indicated the possibility of three-colour heliochromy, and gave a demonstration in support of his theory. Vill THE EDITOR’S INTRODUCTION But after all both Du Hauron and Maxwell no doubt based their ideas on the three-colour vision theory proposed by Dr. Thomas Young. According to his conception the human vision is tri- chromatic, and the fact that most hues could be imitated by three pigments strengthened the conclusion. This theory was subse- quently amplified by Professor Helmholtz. Du Hauron applied it practically to photography, whilst Maxwell was attracted to it asa scientist and proceeded to support it by careful quantitative ex- periments, using photography as a means of demonstrating his conclusions. The leading idea of these early experimenters was that if the eye can see only three colours and forms the other colours of the spectrum by admixture, then the lens of the photographic camera, replacing the eye, must likewise take in these three colours, and the photographic plate is the equivalent of the retina. Thus they argued that if these three colours could be taken one at a time on three separate plates, and the images subsequently reconstituted by projecting them from a lantern or by printing them one over the other on paper, we ought to get a fair imitation of the colours of nature. The basis is thoroughly sound, but the difficulties of carrying out the theory have proved very great. To begin with it was found that the ordinary photographic plate was more sensitive to the blues and violets than to the green, yellow and orange parts of the spectrum. Maxwell pointed out this difficulty and suggested that if photo- graphic plates more sensitive to these last-named colours could be found the results would be improved. There were no colour- sensitive plates in those days, and it was not evident how this diffi- culty could be overcome until 1873 when Professor Vogel announced that the impregnation of the sensitive film with dyes would influence the distribution of colour-sensitiveness in the photographic plate. Du Hauron grasped the importance of this discovery at once, and in his French patent specification of 1874 he mentioned the use of colour-sensitizing dyes. This was elaborated in his English patent of 1876. Given the colour-sensitive plates the next part of the problem to solve was the preparation of suitable colour filters so that only 1x. COLOUR PHOTOGRAPHY light of the particular colour desired should reach the plate at each exposure. This did not prove a very easy matter. The scientist was able to say what the colours of the three respective rays should be, but it was very difficult for the practical man to find suitable coloured glasses or dyes to form coloured films which would pass these rays, and even now the problem cannot be regarded as fully solved. It is accepted that the light-filters for taking should be red, green and blue-violet, but there can be a wide difference in the conception of these colours according to the materials used for pro- ducing them, and only by careful spectroscopic tests can we obtain an approximation of what is best. Having obtained the plates and the filters, the inventors in this field, from Du Hauron onwards, set to work to devise cameras which would form the images successively or simultaneously. It is quite easy, of course, to take three images successively in an ordinary camera, changing filters and plates as rapidly as possible, but such a method will only be successful when taking inanimate objects, and where there is no possibility of the light changing rapidly. The great desideratum was therefore to make the ex- posures simultaneously, and here is where numerous experimenters have exercised their ingenuity, as the subsequent pages of this book wil] show. The difficulty is to get the three images exactly the same size and with the same perspective so that they can be exactly super- imposed. That result has been achieved, but whether by the best means for commercial application remains to be seen. Separating the images by mirrors or prisms has been found full of snares and pitfalls, besides necessitating elaborate and expensive construction in the cameras, with corresponding probability of the apparatus getting out of order. If we can eventually realize Du Hauron’s idea of placing the sensitive surfaces one behind the other, with the colour filters be- tween, like the pages of a book, and use the colour sensitive “ film pack ” in an ordinary camera the method would be ideal. Before that can be accomplished much will have to be done by our dry- plate and film manufacturers. They must give us thin sensitive xX. THE EDITOR’S INTRODUCTION films of the greatest translucency and sensitive to exactly those por- tions of the spectrum we want to record on each of the three sur- faces. The absorption of the uppermost films will have to be al- - lowed for both in the general and colour-sensitiveness, and will have to be controlled or supplemented by adjustment of the inter- posed colour filter films. How far these things are likely to be accomplished can be better judged when the reader has gone through this book. Of course, when we have got the colour negatives right there remains the final problem, perhaps the greatest of all, as to how to obtain the coloured prints from them. As the author shows there are various ways of doing this, and many other ways have been suggested which the author has not thought it worth while to des- ‘cribe because he has not worked them. In the opinion of the writer of these remarks there should not be much difficulty in applying the ordinary methods of colour printing—such as by half-tone blocks, photogravure, collotype or photo-lithography—to the reproduction of good three-colour record Negatives, indeed the means exist now. The negatives must, how- ever, be good in three essentials. They should be equal in size and perspective, should correctly record the colour effect, and have equal photographic density. Most negatives produced by three- ‘colour cameras so far have been sadly lacking in one or other— and in some cases in all—of these qualities. In these directions im- provement must be sought before we can hope to see really successful colour printing, whatever may be the process employed. The process block-maker can as a rule bring about a good result even from an imperfect set of negatives, but he ought not to be expected to do this, and it lays him open to the charge of “‘ faking ” the result. Some amount of manipulative skill in the direction of what is called “‘ fine etching” is necessary with half-tone block making, but this should only be for the purpose of correcting the inherent limitations of the process in regard to tone rendering, not to correct faulty three-colour records. In the case of photogravure, collotype and photo-lithography (especially by graining methods), there is not so much scope for a COLOUR PHOTOGRAPHY “‘ faking,’ and first-class original negatives are essential. Given such negatives there are wonderful possibilities for three-colour printing by these processes, and we may look for the greatest develop- ments along this line. As regards colour prints by photographic or semi-photographic methods it will be seen that the author has the greatest faith in the carbon process, and if some of its difficulties could be overcome— such as those due to stretching of the paper, and the somewhat im- perfect pigments which are used in the tissue—there would be great hope for this method. Processes of using dyed films require a good deal of manipulative skill, and so do methods of toning bromide prints. In fact a really good, easy and reliable process for colour- print making has yet to be evolved. Perhaps the information on the method of producing three-colour negative records as a basis for reproduction as given in this book may point the way. It may be noted by those who are familiar with the various methods of three-colour work in vogue up to the present day that nothing is said about such processes as Autochrome, Paget, Dufay, Omnicolore, etc. These belong to a different category than the methods which the author has sought to expound, and it would necessitate a much larger book to deal with them. Moreover it would be likely to confuse the reader to deal with too many alternative methods of carrying out the three-colour principle. Information about such processes can readily be found in other books. In the present work the opportunity is given to the reader to study very thoroughly one of the most important paths in three- colour photography. The course chosen may prove only a bye- path, indirectly leading to some epoch-making discovery, or it may widen out into a clear and direct way to successful three-colour photography. WILLIAM GAMBLE. X11. THE DAWN OF THE ONE-EXPOSURE CAMERA I CUS bAWr TMD IRS alle THE DAWN OF THE ONE-EXPOSURE CAMERA. colours by photographic means, excluding all handwork, was born with the photographic process. To give the different dates of history appertaining to the applicative development of this new idea for art and craft would be a long story, but an abridged historical note, based on patent-records, may be of general interest. It is the part least known. Photography in natural colours is, as a whole, divided into two main methods: the additive and the subtractive method. The additive method of colour definition is the younger branch, but is nevertheless now considered the foundation on which are based the modern scientific explanations, and from which deduc- tions are made in respect of light, its composition, and its separation into the prismatic colour rays. It is generally agreed that the additive primary colours into which white light can be separated by passing through dispersing prisms, are violet, green and orange. If these primaries are again united by three light projections, white light is formed by the amalgamation. The union of green and orange light alone would form yellow light. If we desire to have a blue light we have to superpose green and violet rays, and orange and violet would show as pink when united. The additive method is the base for the chromoscopic and kinematographic colour projection. The Autochrome and similar one-plate colour-photographic productions are effected by what may be described as a semi-additive method. The older method of colour definition is the subtractive method, and is the one which shows the results by reflected light ; the three subtractive primary or printing colours are blue, yellow and pink, and these three colours when superposed form black. To show the desired colours on the image, we have to subtract, that is to say, we 4 pas attempt to solve the problem of producing pictures in 2 COLOUR PHOTOGRAPHY take away the colours not desired. If we omit to print pink, but print only yellow and blue in superposition or as mixture, we produce green or a colour minus pink. (Pink is often called red, a name that is just as often given to dark-orange, the special red). The combination of pigments and the whole scale of such colours is known to us, and has been used since painting and printing became the means employed for embellishment in our homes and in developing art and industry. It is the same to-day when applied to photographically selected colour records. The first suggestion to use photographic means for making colour representations by photographic colour selection, as embodied in a patent, comes from Ducos du Hauron;* his first English Patent, 2,973 issued 1876, shows him as father of nearly all colour cameras, and his directions for colour printing are still used to-day. His specification of 17 pages can even now be had at the Patent Office, price I/-. . Later inventors have too often neglected to mention, that their wisdom was derived from the teachings of Ducos du Hauron, and some have even denied certain facts, found in black and white in the patent specification mentioned above. Some abstracts from this document should therefore be welcome, especially the one which quotes the suggested One-Exposure Camera. Page 15, part 9 says: | “9g. Principles of Construction of a Triple Camera adapted to the system. Simultaneous and lineal identity of the proofs. ‘“‘ The rays coming from the subject to be reproduced are received upon a glass unsilvered with parallel faces inclined 45°, or thereabouts, in respect to the model and in respect to a first lens, towards which it reflects a part of the above-mentioned rays. The greater part of these rays traverse this first glass, and they are received by a second glass equally unsilvered and with parallel faces also inclined 45°, or thereabouts, in relation to the model and in relation to a second lens towards which it partially reflects the rays which it receives. Lastly, the rays that this second glass allows to pass are received by a third lens either direct or by interposing a silvered or metallized glass which reflects nearly all of them. *Du Hauron died on the 31st August, 1920, in extreme poverty, at the age of 83. He never really profitted by any of his numerous clever inventions in three-colour photography. THE DAWN OF THE ONE-EXPOSURE CAMERA. 5 “In virtue of this arrangement the three images received by the three lenses are geometrically the same. “There are evidently many ways of varying this con- struction without departing from the essential elements thereof, and which I have specified.” Ducos du Hauron does not specifically repeat that light-filters have to be inserted in the different light-paths of this triple camera, CiR hae oy, B|O1A 4ayi4 Green Filter Orange Filter Fa Fig. 1.—Ducos du Hauron, English Patent 2973/76. O, First mirror P, Second mirror. but speaking in a general way, how the negative colour records have to be taken in any colour camera, he says (page 4) : “as to defining for its practical operation the course of the manipulations one may say that they consist: Firstly—In producing in the camera three negatives of the same subject, one by green light, the second by orange light, the third by violet light. , and page 10, what we now describe as light-filters are referred to as the ‘“*‘ manufacture of three sorts of glass or coloured mediums.” I have made a drawing of the one-exposure camera described, believing it to be a great help to better understand Ducos du Hauron’s directions. (Fig. 1). The position of the light filters I take to be interchangeable. 4 COLOUR PHOTOGRAPHY CHAPTER’ Lh: THE EARLY ONE-EXPOSURE CAMERA. INCE writing my last chapter, I found that Ducos du Hauron’s triple camera was patented before 1876, in France on December 15, 1874, and is there registered under Number 105,881. The complete patent specification shows clearly that all his cameras were intended for the subtractive method only, because different methods are given, how to print from the negative colour records in super- position or by pigmentary colours, and no reference whatever is made therein to the additive method of colour photography, that is, to glass positives viewed in an instrument in which the light-cones are coloured by selective light-filters. ‘lq. UeedH Fig. 2.—A. H. Cros, English Patent 9012/89. Antoine Hippolyte Cros, physician, of Paris, patented in England, 1889,—registered under Number 9,012—a triple camera, indicating the same plainly for the additive method only, a system which is now known as the Chromoscope, a viewing instrument pure and simple. If Cros did not invent the name ‘“‘ Chromoscope,”’ but only des- cribed the action of such an instrument, it could not possibly be a reason for withholding from him the acknowledgment that he is the originator, and not a later-comer. THE EARLY ONE-EXPOSURE CAMERA 5 Cros’s Invention seems to have been premature, and little is known of his work. It was quite by chance that I came across his patent application, applied for in England under his patent agents’ name, of which specification I give an abridgment. The drawing (Fig. 2) will explain itself, and it is not necessary to point out the weakness of the system for taking the negatives. I, however, draw attention to the possibility that positives, the negatives for which are obtained by three separate exposures by an ordinary camera, can be shown; and further, if the internal transparent reflector “‘P” is elongated, so that the last light-cone ““ CR3” has also to pass through glass of the same thickness as the others, all the three pictures being refracted alike, we have a fully compensated triple viewing camera (as good as any others invented afterwards), in so far that the irregularities imparted by refraction would be alike in all three picture-paths. The specification says :— ‘“‘ Negatives are produced from the action of orange, green and violet light respectively. Positives are printed from the nega- tives, and to reproduce a picture they are introduced into the grooves for the sensitive plates of the camera behind the coloured glasses. Light being admitted from behind, the images may be seen through lens combined.”’ Our next enlightenment in respect of triple cameras is found in Patent Specification 4606/92 (U.S.A. 475084), the subscriber to which is F. E. Ives, and the abridgment says : “* Camera for producing Multiple Pictures showing the same perspective, the incident rays are allowed to fall on a (trans- parent) mirror O, which reflects some and transmits the re- mainder. The reflected and transmitted rays are again re- flected and transmitted by an arrangement of reflectors and mirrors, until ultimately the rays are reflected from the re- flectors (prisms) to the sensitized plates to produce three dis tinct and similar pictures. The camera also serves to super- pose the several images by vision in a transmitting camera. The complete specification has several illustrations, one of which resembles the drawing shown for Ducos du Hauron’s des- cribed arrangement. The difference lies in that right-angle prisms are as a new element inserted at the three places marked “ Pr” (as illustrated by the smaller side-drawing of Fig. 3); each prism is followed by a lens. No ocular lens, however, is used in this case, but instead a special ocular mirror inclined at 45° is substituted. 6 COLOUR PHOTOGRAPHY This formation throws the three pictures all on one plane, so that one slide will do, instead of three as before, and it is also suggested that an ordinary camera could be adapted, the prisms, lenses and reflectors being fitted on a lens board. Fig. 3.—F. E. Ives, English Patent 4606/92. My drawing (Fig. 3) gives one formation of the invention : ““O” and“ P” are the transparent reflectors; sands. see sie ocular lens (or ocular mirror) which projects the light-rays by re- flection and refraction, in this case, to the three focussing planes. Other variations of this one ocular system are suggested by inserting some more transparent reflectors. A similar instrument to that shown in Fig. 3, omitting the prisms and internal lenses, was also formed, having three different focussing planes, and only one lens, which gives me the opportunity to make the following critical observation, that is, the light-rays do not only pass as shown by the central ray, but the light derived from spaced objects on view is projected by a lens in the form of a light-cone, the diameter of which becomes larger the further away the focus distance is from the lens. The tangent “ T ” is such an ex- ternal ray of a light-cone which is spreading some light on a focussing plane, where only reflected light should arrive. This extraneous light on focus “‘ Fr ”’ would not allow the three pictures to be taken faultlessly by simultaneous exposure. There is another item. In 1892 there were no colour-sensitizers known which allowed such a rapid exposure for the red end of the spectrum as to permit a simultaneous exposure. T he negatives in such instruments have therefore to be taken by other means, that is, in a direct-vision camera, permitting three THE EARLY ONE=-EXPOSURE CAMERA 7 separate exposures in the same focussing-plane. On the other hand, if the light enters the instrument through the three focussing planes, illuminating the three glass positives as suggested by Cros, then no false light can disturb the amalgamation by sight, of the three pictures, into one when observed at the union point of the three light-cones, the one ocular lens. Strange to say the patent specification 4606/92 does not describe or claim any connection with colour photography, and does not say that the three pictures are taken or shown by inserting light-filters, but the construction of such a triple camera cannot be for any other purpose, and in later years has been declared, as the complete solution of colour photography by the additive, as well as the subtractive, method. Later inventors, however, have proved that finality in this respect has not yet been reached. The Inventions patented by White 8663/96, 18875/98, and Shepherd 10993/02 are somewhat similar. 8 COLOUR PHOTOGRAPHY CHA Pith bits THE CHROMOSCOPE in his patent specification, “ there are evidently many ways of varying this construction without departing from the essential element thereof.” In my first article I illustrated the above quoted camera, giving the two primary transparent reflectors ““O” and “ P” as at right angles, but as suggested above, the construction can be varied. By placing the two reflectors parallel we should, of course, not depart from the essential element, and still keep to Ducos du Hauron’s direction how to make a triple camera. This brings us to the next line of thought, and development in colour photography, a direction which has been taken by F. E. Ives as published in his patent specification 2305/95. (U.S.A. 531040), where Ives says : “The term ‘ Photo-chromoscope’ I apply to an instru- ment intended to blend together, by optical means, a series of images of the same subject, which series of images constitutes what I term a chromogram, and which are seen through different- coloured glasses or by means of different coloured lights. “‘ In the present case there is a green screen, a blue-violet screen and a red screen. | ** Each section of the Chromogram consists of a glass or other transparent plate upon which the photographic image is directly produced.” These few sentences copied from the inventor’s Patent des- cription, distinctly show that the invention is for the additive method of colour photography only, as before suggested by Cros. In the larger drawing of Fig. 4, the tangent “ T ” representing an outside light-ray of the light-cone shows the impossibility of using such a triple camera for taking negatives for the subtractive method, nor as a matter of fact for the additive method either. The whole invention is strictly limited to the formation of a viewing instrument. | Dies du Hauron says, when describing his triple camera, THE CHROMOSCOPE 9 For this invention also, the negatives had undoubtedly to be taken by other means, or a camera had to be constructed in a way which is not explained in the patent specification. Several varieties of instrument are given in the same specifica- tion, two of which are in a small size, illustrated next to the principal drawing in Fig. 4, but apparatus made according to them are still less capable of being used for taking negatives. Fig 4—F. E. Ives, English Patent 2305/95. Referring to the larger drawing, embodying the intended in- vention, light-filters are inserted in the different light-paths, one vertical and the other two slightly inclined at about 20°. Why they are inclined is not disclosed in the patent specification, but in later years it was claimed that the slanting light-filters were really acting as compensators for refraction defects. This assertion does not seem very convincing, since we know now that such a compensation has to be inserted at the same angle as the reflector “ O ” or “ P,” that is 45° and not 20° as shown, and I suggest that the slanting to 20° was more likely adopted for the purpose of scattering any pos- sible internal reflection. The inventions patented by Edwards 3615/95, Butler 29353 /97, Butler 4290/05 are on similar lines in which, with the aid of one lens and two main reflectors placed parallel into the camera, three pictures are placed in three different focussing planes. The patent specification 3784/95 (U.S.A. 546889) shows the capability of the inventor to theorize, using his faculties to evolve a _ highly scientific instrument “‘ on paper,” but we can take it that the technical difficulties to bring the apparatus into working existence are such that no optician or mechanic is able to overcome them. IO COLOUR PHOTOGRAPHY The inventor may have been able to make a fixed-focus instrument to his own satisfaction, but to manufacture such an ideal for general use is quite another thing. In this invention there is in short one ocular lens, then an extra lens for each of the three light paths, and countless internal re- flectors, the adjustment of which is an impossibility. It is also not possible to take negatives with this ideal. The patents 15753/99, 12514/03, 25142/12 are marked with the same defect. The last named has also a resemblance to the Cros patent. A battery of three lenses triangularly pressed together forming a “‘trio,”? each with a right-angle prism to throws the respective picture sidewards is a patented proposition of Meyer 7193/97, and a similar trio of lenses without the reflectors is also patented under 14364/99 Pollock. Three lenses in a line, the light-cone of the outer lenses being reflected by mirrors or right-angle prisms and the middle light-cone compensated with the aid of an extra lens, is to the credit of Abney 14623/05; and three lenses on a common long- shaped camera body forming three joint cameras, shows a complete stereoscopic forgetfulness of another inventor, the name of whom is appended to specification 3560.99. These cameras might have been designed to take views from aeroplanes, an ordinary view with foreground being out of the question, the stereoscopic differences would be too pronounced and would show as colour fringes, when the three colour prints were superposed to form a united picture. As something out of the way, the chromoscope described by Barnard in specification 3476/02 is worth describing, it has found imitators without being verified as to the possibilities. This time the two transparent reflectors ““O” and “ P” are formed into a cross placed into a square box; one side carried the ocular lens and the other three sides are decorated with the different light-filters, and the respective positive colour records are placed outside. This invention is remarkable for its perplexities and kaleidoscopic sur- prises. tii te el a REAL INVENTIONS II CHAR ED Rely. REAL INVENTIONS that form the basis of educational knowledge, and on that basis of justification, I will now record the most impossible proposals made for triple cameras, as a warning to others to save them falling into the sameerrors. The ball was set rolling—as the saying is—in the States. It is, however, impossible that the inventor of this ‘ real invention ” verified his theory, neither evidently did his followers. These inventors did, however, one good thing, and only one, that is, they enriched the Government coffers by paying the patent fees. As a preliminary, I may add that Theodore Brown, in 1894, was granted a patent 21406/94, for a stereoscopic reflecting system, in which four mirrors were placed in. such a manner, in front of one lens, that two pictures were projected, through the one lens, to the focussing-plane at the back. It is not my place to theorize here on the merit, of this invention, but simply to say, that the idea as such, was perfectly sound for the aim indicated. For the purpose of colour photography, and the necessary splitting up of the view, to form three pictures, the inventors took hold of this same stereoscopic transmitter, or reflecting device, and placed the same in one form, or another, between the one lens and three focussing planes,to form three colour records. With the help of science disguised as a fairy, and an assurance worthy of a better cause, it was claimed for these new “ inventions” that the pictures were all of the same size and from the same point of view, and therefore not stereoscopic. I have no desire to commemorate the names of these imaginative geniuses, but I cannot abstain from giving six illustrations (Fig. 5) of their suggested absurdities, all of which give in each focussing- plane only one part of a panoramic view, and when these parts are again joined and superposed where necessary, we find that the three pictures form only panoramic part-pictures of one whole picture, which latter could have been taken easier, and with less trouble, with an ordinary lens and ordinary camera. |: a great measure it is the failures and not the ultimate success I2 COLOUR PHOTOGRAPHY An eminent optician, whose name is a household word with every photographer, thought he could do much better, made a large lens and by using a stop with three spaced apertures—that is, he created three artificial or excentric lens centres—thinking to form three correct pictures in three focussing planes by interposing a reflector behind each aperture. He showed his work at a meeting of a celebrated society, but the wisdom came after, he saved the patent fees, so the idea is still open and patentable Fig. 5.—Real inventions. Another up-to-date inventor whose speciality is Colour Kine- matography proposes to use three lenses, one above the other, taking three pictures from three different points of view, but he does not acknowledge that there is any stereoscopic difference between three pictures so obtained. At the same time he claims to be able to insert, ‘‘ well-known means ”’ to efface the effect of “‘ parallax,” but what the means are which eliminate such is not disclosed. But then the term “ well-known means ” found lately in many patent specifications, gives the person saying it, such an air of superiority, and if you yourself don’t know the “ well-known means ” you feel as if you must hide yourself for shame, in not knowing such a simple thing, that is well known. Between us, however, it may be stated that there are no means to correct stereoscopic differences. A new idea’ in one-exposure cameras is indicated in Patent 28920/97. ‘This patent of Bennetto has a slight basis on Ducos du REAL INVENTIONS 13 Hauron’s triple-camera. It is a one-reflector camera. The re- flector is a light filter, in this case an orange-red filter. One plate is exposed by the transmitted light and two plates forming a pack are exposed by the reflected light. This one-exposure, one-re- flector, separation camera, is to my mind, when certain defects are eliminated or compensated, the basis of the possible subtractive colour camera, de facto ; such a camera, size 12 by Io inches, has been used by me. Derivates of this idea are: Lumly 4164/99, who claims Ben- netto’s Camera for the additive method, and Butler 9936/99, who simply joins two Bennetto Cameras together to form a stereoscopic combination. | _ Davidson 10043/o1 had the idea of making the whole thing collapsible, a carrier, holding a falling-out reflector at 45°, and also a falling out plate-pack at 90°, all fitted beautifully into a slide which can be used in an ordinary camera; this is the culmination of sim- plicity. The inventor, after all, seems however not to have been satisfied with it, because his specification 15204/04 proposes a solid and adjusted Bennetto reflector box to be made attachable and de- tachable to an ordinary bellows camera. Pfenninger (25907/06) finds that it requires a refraction compensator in a Bennetto camera and later in 1910 (No. 26609) he proposes a self-compensating re- flector filter. The above referred to inventor, who first adapted the stereo- transmitter for a colour camera, has also tried to improve the Bennetto camera; he advises the insertion of a special lens, to render all rays parallel, before passing through the reflector filter, thinking there would be no refraction defect ; but how if you desire a 12 by Io inch camera? I wonder whether this “invention” has been verified. I defy him to find any picture-focus.. I4 COLOUR PHOTOGRAPHY CHAP Gi aye REFRACTION HEN we insert in a square box a plain glass, not surfaced \ \ or silvered, inclined at 45°, such a glass will act as a mirror, also called reflector, and if such a reflector is also a light- filter, ‘‘ reflector filter ’’ will be the description of the same. If now a light-cone by means of projected light falls on the reflector, part of the light-cone will be thrown upwards or sidewards, and is reflected towards one side of the box; and the other part of the same light- cone will be transmitted, or passed through the glass, to the back of the box. Such an apparatus having one optical centre, but forming two focussing planes, is the simplest form of a one-exposure camera, and is the invention made by Bennetto, of Penzance, in Cornwall. In the early times when glass positives, obtained from three- exposure negatives, were shown in a Chromoscope, it was found that the glass positives would not register. The same happened if by means of a Chromoscope, as first introduced, three negatives were taken; the negatives would not be of the same size, but a clear explanation was in those early times not forthcoming, and it is my special purpose, to demonstrate in the following lines, that it is pos- sible for glass, optical, flat and parallel, to introduce deformity into the picture, which is obtained by projecting a light-cone through such glass. The appended drawing (Fig. 6) “ Refraction through parallel plate ’ gives one all the optical bearings, of a glass inclined at 45°. The lower half shows the “ Vertical Refraction’ accumulative, therefore not balanced. The focus in both figures is taken as 120 points. The central radii are 30. The glass displaces the focus by ten points, and it will be seen that the vertical refraction gives the focus-width six points short. If we adjust the vertical focus also to 120 points, then the focal- length of the horizontal refraction will be lengthened by five points. Without the glass a square, all sides having 120 points, will be formed. If a glass at right angles to the central is inserted, the same square is formed, only the focus is slightly displaced. No square can be ee ee REFRACTION 15 formed if the glass is inserted at unequal angles to the central ray. The difference between the horizontal and the vertical transmission is about one-sixth part of the reflector employed, if we take the reflector to be the standard measure for comparison. Horizontal or balanced refraction. same plan be oe 120 F3 As pil" Ne nae aah EEG ree Daag Vertical or not balanced, accumulative refraction. Fig. 6 —Refraction through a parallel plate inclined at 45 degrees. If we copy an exact square through the glass which is inclined, the copy will not be square, but oblong, and no shifting forwards or backwards, no inclination of the focussing plane, will correct the 16 COLOUR PHOTOGRAPHY defect of foreshortening or pressing together of two opposed sides in the formed picture. This defect is generally referred to when spoken of as a “ refraction defect.” If we place the two reflectors parallel or at right angles to each other, as directed by Ducos du Hauron for his triple-camera, or by Prism Base down Refraction . Chhihaabahehl Lh hbbk — Prism Base up ec, | Vi Pe Refraction ao PC ee ot ee ee Fig. 7. Ives in his Chromoscope, or by others, we do not diminish or com- pensate this defect, but we multiply or increase the same, and we do the same with each other addition of light-filters and reflectors if inserted the same way as indicated above. Therefore, such cameras are absolutely of no use for the subtractive method of colour- photography, a method which requires three negative colour records of the same size. Eee REFRACTION 7 Speaking of refracted pictures and displaced focussing-planes, I have also to allude to ‘“‘ Prism base down refraction ” and “ Prism base up refraction ” (Fig. 7) and the displacement of the light-cone such interposition is causing. The focussing planes obtained without refraction F 1, with parallel Plate Refraction F 3, and the re- fraction with the wedge F 2, are given in the drawings and show the difference. The focus planes are given as of same length and in parallel displacement. 18 COLOUR PHOTOGRAPHY CHAPTER VI. PRISM SEPARATION S I have said before, it is by failures that we gain our know- A ledge, and they guide us to improvements. If I give some of the vagaries through which the early workers had to wade in the search for a workable one-exposure camera, the knowledge of these failures may still be instructive, and may well serve as a basis for future experts. It was in the beginning of 1904 that a patent was filed, in which by the aid of two wedge-shaped prisms placed in front of one lens, two identical pictures by the dispersive powers of the prisms were to be formed at the back of the one lens, and by the aid and inter- position of light-filters the negative colour records were to be ob- tained. My drawings show the possibilities for a camera having a two-picture focus only. The defects would obviously be exag- gerated in a formation showing how to obtain three separate pic- tures, so there 1s no need for me to discuss the latter case specially. Tae at ar ae Sai ee ~. + ~ “RR b eS UREA Toft I A Fe “c © b Fig. 8. Exterior Prism Position. Taking the “‘ Exterior prism position ” (Fig. 8) first, the prism placed as an ocular will see not less than from “a” to “e,” and re- fract the passing light-rays towards its base ; the axial ray from “ c ” will be deflected about 2/3, that is if a prism of 15° is used, the de- flection will be about 10° therefore one axial ray from “‘c” will be deflected to “‘c 1.” This formation is also liable to project ghost pictures, the ray ‘‘ RR 1,” from “‘e” arrives aS) k=) see that is, on the picture-plane, where the second prism “P 2’ should form the second picture. The two pictures obtained by such eee PRISM SEPARATION 19 a formation, as to graduation, are shown in ‘“‘ F 1” and F 2,” of the smaller drawing and I specially draw attention to the ghost marked “e.’? This ghost-picture can be made less dangerous, if the space “a e”’ is covered with dark non-reflecting materials. UJ N N N XN N N N N) N N a N N N NY s N N N N N N N N Z Z Orrd: Fig. 9. Interior Prism Position. Instead of placing two prisms, base to base, in front of one lens, we can also insert two prisms, apex joining, at the back of a lens, between lens and focussing plane, as shown in my drawing “Interior prism position” (Fig. 9). This arrangement has the advantage, in not permitting any light-rays to transgress over the optical axis, which passes from “O” to “d1,” because all light- rays passing through such a prism and being part of a direct light- cone, collected and projected by a lens, will be refracted and thereby deflected towards the base of the prism, the formation of any secon- dary pictures or ghosts, on the other side of the axis, is impossible. In the little side drawing, the graduation imparted by the action of the prisms on the two pictures in focus “ F 1” and “ F 2” is illustrated, showing such pictures in superposition. If ‘“ F1”’ should represent a red picture and “ F 2” a blue picture, then, in the united picture, the red would predominate near “ b c,” and the blue near “‘c b’”’; obviously not a very desirable solution. In all prism systems, having wedge-shaped prisms, a certain want of sharpness will be imparted to the pictures, caused by the dispersion of the passing light-rays, and also as with all interposed heavier refracting material, a certain displacement of the focus plane will take place. It has been recommended to separate the prisms, so that a third picture between the two deflected pictures could be obtained. This supposed invention is defective, in that the central picture will 20 COLOUR PHOTOGRAPHY be at a different focus distance, and also of different size, as compared with the other two pictures, and all pictures are only connected together by what I may call prismatic and panorama-like continua- tion, and I am not sure if stereoscopic differences are not present. There is one predominant point which puts all cameras having wedge-shaped prisms out of court, and that is, such cameras would allow the taking of very small pictures only, therefore even if in all other respects the negatives were satisfactory, the size would not be useful for the subtractive method of colour photography. An additional drawing (Fig. 10) shows different light-rays entering a prism of about 30°. After the first refraction by surface “Sr” each white light-ray takes a new direction for the different colour rays, which come to view as spectral colours, after having passed refracting surface ‘“‘S2.” The light-rays can also enter the opposite way, when the spectral colours will naturally also be seen the other way, but the main direction ot each light-ray would be the same as here given. _— EXCENTRIC PROJECTION 21 CISUA PIMOS 2 Oe EXCENTRIC PROJECTION a lens. We can make a camera, and by means of reflectors or mirrors, form two or three focussing planes, each of which ap- parently receives the same amount of light-rays from that one lens, but when we try to form identical pictures, at the back in each separate focussing plane, then we find the same derogatory influence prevalent, as when wedge-prisms are employed. That the whole dividing proposition for the purpose claimed is a fallacy, is demonstrated very easily and conclusively, and I cannot understand that opticians and scientific instrument-makers, known all over the world should have staked their reputations on pro- positions touching their own trade, without verifying their state- ments, by a simple test in the camera. If even experts have lost their bearings in optical knowledge, appertaining to their own pro- fession, I must conclude that others only interested in such researches, must also be at a loss to understand, the effects and causes of splitting up a light-cone. I hope, therefore, to be kindly excused if I state my negations, and to do so my helpmates, photographs and drawings, will give the most convincing support. |: is very easy to divide a light-cone into two or three parts behind Fig. 11.—Sky screening. In an ordinary camera I introduced, not a transparent or re- flecting mirror, but simply a solid block, in such a manner, that the lens was half covered, up to the optical axis (see Fig. 11), then I photographed some printed matter from the Nineteenth Century (see Fig. 12), but so that the black line corresponded to the optical axis and the inserted block; and in the photograph it is seen that the word ‘“ Century” is fully and correctly reproduced, but the 22 COLOUR PHOTOGRAPHY other half is shaded off, because not all light-rays go through the optical centre ; there are light-rays, which pass the periphery of the lens, as shown by the broken line arriving at “‘d” (Fig. 11). If now h Century ge Fig. 12. Sky Screening. we place a reflector or mirror in exchange for the block, is it to be believed, that the word “‘ Century ” would then wholly or partly be reflected in the other half and substituted for ‘* Nineteenth ” ? Anyhow, that is what was expected and asserted to be the case. i *mae Fig. 13.—Panorama-like continuation For those to whom the foregoing explanations are not yet sufficient, I add a drawing ‘‘ Panorama-like Continuation ” (Fig. 13.) The two mirrors “ M1” and M 2” divide the sight into two EXCENTRIC PROJECTION 23 parts, and it is immaterial, if the part-picture is reflected by the re- flector “‘ R” or not, it will remain a part-picture, and the two-focus pictures are therefore, each furnishing only half the picture, necessary to form one continuous whole picture, which latter could have been obtained more easily with one lens in one focussing plane. The exposure graduation, of the two part-pictures and three part-pictures is also given in the smaller illustrations in the same figure, to show conclusively that such pictures are not alike to, and will not, superpose. The pinnacle of ingenuity in ‘“‘ inventing ” an “ invention ”’ is, however, reached with the proposal, to form three separate pictures, by the displacement of the optical centre in the one lens, by means a DMNNMSSFEKK™bh Fo Fig. 14.—Peripheric projection. of three excentric stops. The illustration of this proposition “ Peri- pheric projection ” (Fig. 14) shows really more than the lens can transmit, but is what the inventor thought could be done, and if it had been possible, then, stereoscopic differences would have come to light, because the two blocks “a” and “c” are seen in a different aspect, as when photographed at equidistance from the lens centre. A lens has great likeness with the behaviour of wedge-prisms, which likeness we specially notice, when photographing an object with one lens, into which latter we have inserted an excentric opening; the distance “ a, b, c,”” when reproduced, is curtailed at the most re- fracted side of the light-cone, so that the two pictures “‘ F 1” and F 2” will never completely meet as shown in the graduated scale. This curtailment of the graduated scale depends, somewhat, on how 24 COLOUR PHOTOGRAPHY far the artificial lens centres are placed away, from the actual or natural optical axis, but it is certain, that wherever the excentric stops are, they do not eliminate the foreshortening defect. The smaller triangular illustration shows in a general way, how the three pictures obtained in the three focussing-planes “‘ F 1,” “ F 2,” F3”’ fit together, and how far they superpose. I have an idea that three lenses placed close together, passing. as little stereoscopic differences as possible, would fulfil much better the requirements for a triple camera for the subtractive method of colour-photography. Similar misapplications in optics exist also in the spectacle trade. When you order bifocal glasses all tests are correctly made through the centre of the test lenses, but the manufacturer without any misgivings transposes the action into a peripheric one and if you see colour fringes, he stoutly disclaims any liability or the possibility of such a thing. DOUBLE REFLECTIONS 25 Cra Er Re VILE. DOWUBEE REFLECTIONS refracted picture, but we have also to know what happens on the other side of the glass, used as reflector and filter—we have to know the crucial facts of the reflected light-cone also. { N one-exposure cameras we have not only to account for the Cc eS ee Bl mean PINS EN ae ol a cater Fi a ibi Ly \ i : ' | | ( ( | | ! \ 1 ye ; ‘ 4 LLL CALLE LLL Fig. 15.—Ordinary reflection. If we follow, as shown in the drawing, “ ordinary reflection ” (Fig. 15) the rays “‘ L,” part of the same will be reflected by the first surface “‘ S 1” of the glass to a first focus “‘ F 1,” a second part of the same light-cone will pass and be refracted by the same surface “S11.” The refracted light-rays “‘ R ”’ will be deflected to the back or second reflecting surface “‘ S 2,” where the same partition of the light-rays is repeated, and the reflected rays “‘ r ” are again refracted on their return to the first surface “‘ S 1,” and eventually come to a second focus in “‘ F 2,” which latter is about half a glass-thickness inwards, or shorter than the main or first focus. The secondary light-action will however, pass over the inner focus plane, and on arriving at the exterior focus plane will show to 26 COLOUR PHOTOGRAPHY some extent as a secondary picture, if exposure is made on a photo- graphic plate. This weaker or second picture, if slightly less sharp and displaced,must be elongated when it arrives on the focussing-plane of the first and direct reflected picture, contrary to the refracted and fully transmitted picture, which latter is partly narrowed down. The secondary reflections are also subject to what is called *“ spectral dispersions” and this latter would also influence the sharpness of the secondary picture. Granted that these rays are slightly out of focus and unable to form a very sharp picture, they would as ghost-pictures seriously interfere with the true picture formed in the main focus by the direct reflected and, therefore, predominant rays. We have means to suppress the secondary actions of these rays- We can make them non-actinic through absorption and by using photographic plates which see only one colour. In a one-exposure camera the best white optical glass covered as a rule on one side with a vehicle holding colouring matter is used for the reflector or mirror, and is often referred to as transparent, MUTT ETTETEMA ESTES. CLT TLLLL LLL Fig, 16.—Prism base up reflection. reflecting, transmitting, refracting filter or reflector. The vehicle is generally coated on the second surface, and if red would impart red on the secondary picture, and absorb the blue light-rays to a very great extent. DOUBLE REFLECTIONS a7, The interposition of a red light-filter, acting as reflector-filter, will affect in a similar way the transmitted light. It will absorb the blue rays, even in the prismatic dispersion which is introduced through the first surface. For the purpose of absorption of the blue Fig. 17.—Prism base down reflection. rays in the secondary reflection, a reflector coloured in the glass, is still better; such a reflector must, however, also be faced with a “coloured vehicle’ in such a manner as to fully correct the filter for the transmitted rays. Silvering, platinizing, varnishing, etc., of the first or main reflecting surface has been advised to augment the amount of re- flected light, and in order to eliminate the double reflection, but if applied, only surfaces are introduced, which are subject to tarnishing and gradual loss of reflecting power, and this on the very surface, where stability of reflection is the predominant desideratum in such a reflecting system. . It has been suggested by Ives to use wedge-shaped prisms to disperse the double-reflection. I have made two drawings— ““ Prism base up reflection’ (Fig. 16) and “‘ Prism base down re- flection ’ (Fig. 17) to show that this very scientific suggestion simply displaces the secondary focussing plane and that in certain parts Boumeroc of 1 and ~“F 2” touch each other, giving there a much better impression of the secondary picture than parallel plate could ever give. 28 COLOUR PHOTOGRAPHY If, however, we consider that wedge-prisms, of much lower degrees as shown in the drawings, can possibly be used, then the introduction of such prisms seems of doubtful utility, and they be- come positively harmful to the transmitted pictures, which is ascer- tained when the consequences of refraction have to be drawn for that purpose. When we come to camera systems with several internal re- flectors, we must consider the consequences and have some idea as to what internal reflections will do, say only between a few parallel surfaces of glass. To come to a sufficient understanding, I can suggest the following :—Sitting in a tramcar at evening time, you can easily admire yourself or the lady at the furthest corner, or you can see what is going on or passing in the street, at the back of you, or in front of you, and all this whilst sitting perfectly still and losing yourself in the kaleidoscopic reflection. Further, imagine what the addition of some more reflecting surfaces may bring about, and apply the conclusions to the reflector systems of cameras, and you will understand much better than I can tell you, why reflector One- Exposure Cameras, with more mirrors than one, are only theoretical illusions, and scientific experiments applied ad absurdum. INCORRECT REFLECTIONS 29 SARE R Lx INCORRECT REFLECTIONS reflected from a plain reflecting surface would, on arriving on a focussing plane, give a correct representation of the respective projected image of which the lens is the medium and the light-cone the optical field. The interposition of a reflector, con- sisting of a glass from one-tenth to one-third of an inch, does not really affect the transmission very much; if a smaller stop is used the introduced unsharpness is not noticeable, and only a trained eye would see the small displacement caused by a glass when placed at an angle of 40 or 50 degrees into the light-cone. The refraction defect imparted is so very small and by some experts is even now declared to be an illusion and non-existing. A glass placed as suggested above and as used 1n a one-exposure camera plays, however, undeniable havoc with the reflection if in the slightest way out of its proper position. It alters the focussing direction. In my drawing “Incorrect reflections” (Fig. 18) the light- cone coming from the optical centre ““O”’ is reflected by the re- flector “‘R 1” inclined at 45 degrees and arrives at the focussing- agent o. | Lhe central: ray of this cone “ C 1” is reflected at the pivot ‘‘ P ” and arrives at ‘‘ d”’ when the two half-cones “ bd” and “‘ df”? are shown to be of equal or balanced width— 4o points each side—therefore together 80 points. As an alternative, if we now give the reflector an inclination, of say 40 degrees, ‘‘ R 2,” then the central ray ‘‘ C 2 ” also passing over “‘ P” will, on arriving at the focussing-plane “‘ F 1” be dis- placed to ‘“‘c.”” When we find the “ a-c”’ half-cone 44 points wide and the other half-cone “ c-e”’ only 40 points wide, the full cone covering therefore 84 points of the original focus plane “ F 1,” is therefore not balanced and is occupying more space. This irregu- larity would show itself in a picture as unsharpness, being out of focus at both ends, similar to a badly adjusted swingback, a thing, | i to now we have taken it for granted, that whatever was 30 COLOUR PHOTOGRAPHY by-the-by, that cannot be used in a camera with more than one picture-plane. On the other hand, if the reflector is inclined at 50 degrees ““R 3,” exactly the same irregularity takes place, but the larger LITT 72 CLLILITLLTTELTT) O Fig. 18.—Incorrect reflections. — half-cone is now towards the “‘ g ” and not towards “a” as in the second case. I have to point out these irregularities, because the camera being once constructed, cannot be altered, only the reflector can be moved and in doing so, one may easily under or overdo the packing on one side more than the other. If, however, the focussing planes for F 2 or F 3 can be adjusted at right angles, to the central ray “‘ C2” or “‘ C 3” respectively, then the two sides of the light-cone will be balanced as in the case of. focussing-plane “‘ F I ” in connection with the ray “ C 1,” but as I said, if the focussing planes are once fixed then no such alterations are possible to the person not initiated. An American inventor has filed several patents in which he introduced a plain transparent reflector inclined at 45° to the central ray. I have also inclined such a glass in my camera and upon trying to find the focus I came to the conclusion that a real photo- graph of the observed phenomenon would speak much better of the INCORRECT REFLECTIONS 31 value of the invention than anything I could say. It had evidently never been tried before the patents were obtained. The two photo- graphs (Fig. 19) were taken simultaneously in a one-exposure camera Fig. 19. Refracted picture above; Reflected picture below 32 COLOUR PHOTOGRAPHY having a plain, not coloured, reflector. One view is by refraction and the other by “‘ double ”’ reflection. If, on the other hand, the reflector filter is of yellow (or green) glass coloured in the mass, yellow would be reflected by both sur- faces and if such a reflection impinged on a yellow sensitive or panchromatic plate, similar double exposure would result. It seems to me worth while to know all these little intricacies the one-exposure camera work is heir to. We are all so liable to take many things as obvious, and if you try to disprove an “ obvious thing ” you are often called a fool. CURVED SURFACES 33 CUS DAM OTT BIN Oe BukVEDS SURFAGES VES in his patent 2305/95 inserted plates at 20 to 25 degrees [ inctnstion, and describes them as light filters, but for what purpose they were so inclined is not disclosed, perhaps to over- come internal reflections. (Twelve years afterwards he based a claim on this position stating the same to be a described compen- sation for the refraction defects.) But only four years later he filed a compensation patent in the States. Fig. 20.—Reflection and _ refraction. Curved parallel surfaces. On the fourth day of April, 1899, letters patent numbered 622480 was granted to Ives in the United States, describing and claiming a.method of distorting the reflected picture also by the application of local pressure to the reflecting surface of the trans- parent mirror by means of springs or other pressure devices. The English patent 3872/13 is for “ other pressure device ” granted to the Dover Street Studios, no application being made for same in the States. My drawing ‘ curved parallel surfaces”? (Fig. 20) shows in exaggeration the effect of pressure applied to the reflecting surface 34 COLOUR PHOTOGRAPHY and it is evident that more distortion pure and simple is thereby in- troduced, therefore no correct compensation, for the simple reason that no pressure device could ensure an equally balanced pressure all over the reflector. The drawing shows that the reflected picture in the focus, when the hollow or bent side is facing the lens, is narrowed down from 80 mm. to 65 mm. as compared with the original focus, and is also curved in at the focus plane, and at the same time the refracted picture is widened out, from 80 mm. to 95 mm. (3} to 3$ ins.) with the curved focus in the opposite direction. This curvature can also be placed in the hollow or bent side away from the lens, when the reflected picturewould be larger,and the refracted picture smaller, and the curvature of the picture would also be reversed. If this curvature is imparted cylindrically, the picture would be deformed in that direction only, and if the curvature forms parts of a globe, then the image would be affected that way. I think I am right when saying that if such curved reflectors are inserted into cameras, and the focus is adjusted for one lens and one distance, then a fresh adjustment is required if employed for a different distance, or if another lens is inserted having a different focus. Therefore only cameras having a fixed focus could be em- ployed if such pressure device is to be applied with success to the reflector. The above are the only two known patents claiming the cor- rection of the reflected picture only, so it is still open for an inventor to patent the correction by way of refraction-distortion, but before losing his money in a patent speculation, I advise him to have a good look into a mirroscope having a cylindrical mirror, or to admire himself in a silvered globe, optical appliances which have been patented to obtain distorted photographs as claimed in Patent 22825/08, by Hamburger and Costen. The circular distortion with globe-like surface can also be obtained without any pressure device, if a thin glass reflector is covered with a contracting vehicle, such as gelatine, when dry. This substance being hygroscopic, has to be protected, but even when protected could as little be depended on as the mechanical distortion device named above, and this idea is not patented yet, nor are the following ones. A slanting glass reflector, if thin enough, will sink in towards the centre if fixed in a frame, similar to a blanket hung up at the different corners, or the same glass reflector will a — CURVED SURFACES 35 bend cylindrically if only fixed on one side, so that the main body. stands out sideways in the camera, and we must not be surprised to hear one morning that a collodion film stretched over a frame has been suggested as a reflector. In the above I have not touched on the atmospheric influences, the expansion by warmer, and the contraction by colder surround- ings, and I think there is no doubt that such influences do not make for stability of the reflecting surfaces in any pressed or coated re- flector-filters. The tension exerted by a gelatine surface is noticeable in a 12 by 10 inch plate, having a thickness of one-eighth of an inch. 36 COLOUR PHOTOGRAPHY CHOAP PERG OE SOME COMPENSATIONS ONTINUING the enumeration of the possible compensa- tions in one-exposure cameras in which the light-cone is refracted, I now have to deal with Ives’ device of compen- sation with right angle prisms, a device that once had been recom- mended for viewing stereoscopic pictures. The illustration (Fig. 21) shows, that the geometrical condition forming two focussing planes of same size with paired and equal Fig. 21.—Compensation with right-angle prisms. refraction is really the accomplished fact; we have to ascertain if the scientific proposition is also fulfilled. Seeming facts are often negatived by further investigations; the paper is very tolerant and the patent office is always glad to take the money, even if the inventor has not verified his facts. A prism combination as here proposed will not form a picture in “ BF” at the back, but only in ~ TP thetope onesie ee hand, if the two prisms are cemented together, then no internal reflection to “TP” takes place, the two prisms simply forming a cube in which the picture is only visible at ‘““ BF ” and that very likely slightly displaced, the Canada balsam being of a slightly different density. To form a picture in each proposed focussing plane we must have one of the surfaces silvered, where the prisms join each other at “P.” The silvering has to be balanced in such a manner as to be partly transparent and partly opaque, and when that is attained it requires a conjuring trick to cement the two. parts ———— a SOME COMPENSATIONS 37 together with Canada balsam, without injuring the silvered deposit. When all this is accomplished, it will be found that the refraction defect has not been completely eliminated, and that a slight dis- placement of the back-picture is still present, therefore, giving an incorrect picture. Even if the compensation worked completely and correctly, what about the loss of light and the cost? The latter would be prohibitive even for a quarter-plate camera. The whole proposition resolves itself into a scientific plaything of no value whatever. The inventor gained thereby, no doubt, the scientific halo of being a very clever man. Fig. 22.—Wedge Prism Compensator. The investigation of wedge prism compensation is our next proposal (Fig. 22). We have seen in a former article, that in the ordinary way, when using parallel plate as a reflector filter, the difference of the refractions at R 1, and R* 2, is the cause of the pressing together of the light cone forming the back picture, and it was suggested, to make the refraction at R 2 of the same length as at Ri. If we adopt that proposition, the two surfaces of the re- flector will no more be parallel but convergent and the reflector will have the appearance of a wedge, 7.e., narrow-angled prism. I should think such wedge prisms in larger size would be expensive and the complete problem would only be solved for a fixed focus camera. For each lens and for each different focus distance another wedge prism has to be exchanged, calculated for that very focus required. Moreover, the refractive displacement of the picture at the focussing plane has also to be investigated. There are altogether quite enough disabilities, to justify us in dismissing the wedge prism compensation, as of no use in one-exposure cameras. The wedge prism has, however, also been advocated by Ives for the specific purpose of dispersing double reflections, which was dealt with in Chapter VIII. 38 ' COLOUR PHOTOGRAPHY A curious, but scientifically correct self-compensating action (Fig. 23) has been patented by O. Pfenninger. Fig. 17 of Specifi- cation 26609/1910, of which I give an illustration, embodies the invention. | Fig. 23.—Colour camera with self-compensating reflector. English specification 26669/1°. The lettering r-s-t-u shows how the reflector in a Bennetto Camera is placed. The present way of placing the reflector is shown, and marked v-e-f-u, which position places the refracted picture over the diagonal a-c. The foreshortening is therefore equal on the sides joining each other a-b and a-d, and the whole refractive action is only by accumulative refraction, described in Chapter V. The reflection is also thrown sideways and necessitates the peculiar shape of the camera box. It is said that this patent has been partly acquired for U.S.A., and the patent is accepted by the United States Patent Office without opposition. It is very interesting to know that this is the camera which Dover Street Studios used in I9I11I-13 in taking successfully by instantaneous exposures three correct colour negative records, size 12 by 10, the illumination being a magnesium flash. For the Polychromide printing process used in the same studios, carbon pigments were at first used, with an alternative for the yellow, for which a bromide print was toned (converted into) a yellow print with mercuric iodide. BENNETTO’S SYSTEM AND COMPENSATION 39 GEAR IER xl): BENNETTO’S SYSTEM AND COMPENSATION camera system, English patent 28920/97 (Fig. 24). The system is on the simplest lines possible, having only one reflector. It is, therefore, an absolutely independent invention, free of any anticipations and cannot be ranged with the two or three reflector systems. Since it has been proved that this is the only system with a future, other inventors have claimed the same as being included in patent claims of the older systems, but I have looked up all the different patent specifications relating thereon, and they all speak of “‘ reflectors.”” Now in two Bennetto cameras there would really be two reflectors, but only one reflector in each separate camera. ‘ LREADY several references have been made to Bennetto’s Fig. 24.—]. W. Bennetto’s Patent 28920/97. In Bennetto’s system, one light-filter ““P”’ is introduced as a reflector filter, and is inserted at an angle of 45 degrees into a box, in such a manner, that the light cone is reflected to the top “‘ TP,” to form a focussing plane. The reflector filter is however transparent, and some part of the same light cone, is passing through the same reflector filter to the back focussing plane “ BP,” this back- picture being foreshortened as already explained. (Page 15). Bennetto’s original system is not well adapted for the sub- tractive method, because a casing, to eliminate the extraneous rays, 40 COLOUR PHOTOGRAPHY is not provided. We have, therefore, to use an “‘improved one- reflector camera ”’ system (Fig. 25) for taking negatives. These two systems. can be used for the additive method, but even with such Fig. 25.—Improved One-Reflector Camera. an improved system we do not obtain pictures of the same size only a picture that is clearly transmitted and a picture that is clearly reflected, with the help of block “‘ BE.” The ‘“‘ Compensated Bennetto Camera,’ (Fig. 26) English Patent 25907/06, by O. Pfenninger, shows us that when inserting a compensation plate, in preference, to the refracted light cone, the inventor obtains two equal pictures, because he inserts a compensa- tion plate in the refracted light cone, after the reflector filter, in such a manner, as to obtain pictures free of any distortion. Fig. 26. Compensated Bennetto 25907/06. If a-b-c-d is the upwards inclined reflector filter, then e-f-g-h is the sidewards inclined compensation plate, inserted so that the picture, already compressed and refracted in one direction, is a BENNETTO’S SYSTEM AND COMPENSATION 4I second time compressed and refracted, but in the other or cross direction, the inclination of the reflector and the compensation plate being the same, and the two plates of the same thickness. This compensated system furnishes two picture planes, of which the back picture is narrowed down horizontally, as well as vertically, to the same amount, but both picture planes are of exactly the same form, and to bring them to exactly the same size the back focussing plane has to be adjusted by being placed further away. The dis- tance of displacement is about + of the thickness of one of the plates. This displacement of focus is necessary to obtain a picture as sharp as the top-picture, because the refraction displaces not only the focus as to size of picture, but also as to sharpness. When the camera is worked, a pack of two plates, film to film, is taken in one focussing plane, and one plate in the other focussing plane. The filter arrangement and the respective focussing planes naturally depend on this, and are a matter of pre-arrangement. From the negatives obtained with the improved Bennetto camera, it would, with the aid of slanting and upright parallel plates in the copying apparatus, be possible to make corrected glass posi- tives, but it is preferable to take the negatives in the first instance with a fully compensated camera. 42 COLOUR PHOTOGRAPHY CHAP TER. XT COMPARATIVES AND ANOMALISM_ IN REFLECTOR: CAMERSS especially as applied to colour-photography, seems desirable and I hope may be instructive. In a general way we are always informed of all the “‘ expected merits’ of an invention, but when the expectations have broken down, nothing further is heard of the same, and this is only too often a sign that the inventor lost himself in “ theoretical suggestions ”’ before applying the “ practical test.” The press, always eager for *“ copy,” publishes the information or news without regard to cor- rectness, originality, possibility, etc. My specific intention is to have a peep behind the curtain of lost expectations in respect of reflector cameras. So far back as the sixties it was recommended to place a solid or translucent shield at a certain distance in front of the lens when photographing a landscape, so as to shade off the sky. With such a medium it is possible to shade off the plate from the centre so as to be transparent on one side. In the studio the same idea is now used. A vignette, or a part of a vignette, cut out of translucent or opaque material is placed before or behind the lens, ata certain distance to obtain the white or dark vignetted pictures now in vogue. The latter were first shown at the International Exhibition, Paris, 1878, by a court photographer from Petrograd, and awarded the Grand Prix. Two opaque flaps (not mirrors) in connection with one lens, are placed so that one exposure of a person could be made on the left side of a plate and a separate second exposure of the same person on the right side of the same plate, showing afterwards as “ self shaking hands with self”; this is a similar application of the sky- screen idea. ‘ CRITICISM on reflector cameras in an objective way, Since 1899 a multiple of this sky screen in one way or another forms the corner stone of some inventions for reflector cameras. Oe a ee a oa COMPARATIVES AND ANOMALISM IN REFLECTOR CAMERAS 43 The first intimation of this extraordinary invention came from the United States of America. In this invention the halving of the light cone in front or at the back of a lens (as shown above), is not done by two flaps, giving two “ different pictures ” by two exposures, but by means of mirrors or prisms, and duplicates “‘ all alike ” of one object at one exposure are now said to be obtainable. There are several different inventions on the same line of thought standing to the credit of that American inventor. Now I grant that by these means it is possible to obtain several illuminated fields or a “ different”’ picture on each field at one exposure, but the same amount of picture of the “‘ same ” subject in all fields.as required for a one-exposure colour camera is “ unattainable,” at least on this side of ‘“‘ the pond.” Perhaps the light and optical conditions are different on the other side, and the light rays travel round corners, not through the centre of a lens. The first whisper of this new colour camera encouraged other inventors in the old countries, not suspecting tall stories, to enter this sky screen competition, which became keen, and several dozen patents vouch, not for the acuteness of these inventors, but for the money paid to the State. These discoveries all belong to the paper inventions. There is no doubt that they are “ real inventions ”’ of over-smart people, because the facts of real possibility were never verified, and I doubt if any of these suggested cameras were even constructed, because if they had been, the fallacy would have been only too apparent. As it is a certain halo as a compensation is still attached to these pioneers of failures. The principle of Bennetto’s system, the one reflector camera, has lately come to be recognised as the nucleus for a one-exposure camera. It is now known that the light reflected in such a system is about one-ninth part of the light cone; the absorption of the transmitted light through the orange-red filter 1s about six-ninths, leaving a two-ninths part of light to act in the direct light cone. To meet this difference between the reflected and transmitted light action, it has been recommended to silver or platinize the reflector. If the surface of the glass is too strongly metalled, it will be too opaque, preventing the passage of light, and if the metal surface is so thin and transparent as to balance the transmitted and reflected light action, then the metal coating has no resistance to withstand the polishing pad, and if varnished will not present a better reflecting surface than the ordinary polished glass. 44 COLOUR PHOTOGRAPHY Cross-cutting the metal surface so that the surface resembles a half-tone screen introduces defects similar to the following in- genious device, which is, a part-perforated reflector-filter, and it looks perfect on paper, but if dissected, it simply amounts to the placing of several (say 10 to 20) sky screens or “‘ vignettes Russe” to the square inch. The glass in the perforated, and therefore transparent, parts eliminates the refraction defect to perfection, but what about the action of the perforated screen on the photographic plate ? Let me apply the conditions of a ruled screen (to which the perforated screen is akin) of the half-tone process worker to a quarter plate one reflector camera actually in use. The data is as follows : Camera extension 18 cm., and a variant of 25 cm., focal length. The light cone passes through the reflector filter, which is inclined at 45° when the extreme light rays would give about 5 cm. and 12 cm. screen distance. The screen opening, that is here the perfora- tions, we take for one calculation to be 1 cm. and for an alternative 4 cm.; in which case the stop required for a half-tone dot is found as follows :—The calculations being made in millimetres. Screen Camera Screen Size opening. extension Sum. distance. ' of stop. 10 x 180 = 1800: 50 = 36 mm. 10 x 180 _ 1800 "22 atae = L5iae. 5 x 180 = goo : 50 == IS 5 x 180 eS 900° aaeei2o oe 7 Se IO x 250 = 2 500M 50 = 50. 4; 10 x 250 = 2500 = wier20 om Zl os 5 x 250 “= 12501 50 = 25 Cass 5 x 250 a 1250) [reo = IOs s; A 25 cm. or I inch stop is as seen a good size stop for general use or under above conditions for half-tone dots, and a smaller stop would allow a still greater screen distance, or would accentuate the screen pattern on the plate still better. If the perforations in the reflector-filter are larger than the stop, then no perfect dots would be formed by the light, but some pattern of the screen would still be imparted. It is noticed that at one end of the plate the condi- tions for a half-tone dot are perfect, the slanting perforated screen would naturally impart a certain degradation and the plate would _ COMPARATIVES AND ANOMALISM IN REFLECTOR CAMERA 45 present a certain irregularly spotted pattern, but never a uniform picture. What about the reflected image ? Well, the same will represent exactly the reverse appearance to the transmitted image and also in exact proportions to the missing or cut-out reflecting surface. If you look in your own looking-glass having a hole in it, or an Opaque paper patch on it, it will prevent you seeing yourself to the extent of the missing reflection, and if you hold an opaque patch between you and the mirror (like a sky screen) it will by no means improve the reflected image—it is all so obvious—and yet, when applied to a photographic camera, specifically for colours, Munch- hausen or Don Quixote rushes into print, feeds the Patent Office with cash, defies the optical laws, boasts of special scientific know- ledge, and thoroughly wastes his energy. 46 COLOUR PHOTOGRAPHY CHAPTER XIV. ADDITIVE AND SUBTRACTIVE LIGHT PROJECTION. manifested itself to take three negative colour records for the subtractive method ; an easy photographic printing method does not exist even now; the carbon printing is still the best, but the photo-mechanical process by three-colour blocks has made impor- tant progress, and it is for this means that three colour negatives are in demand. | I think it advisable, therefore, to illustrate the camera required for the additive as well as for the subtractive method of colour photography, and indicate the requirements and differences between the Du Hauron-Ives Camera and the Cros-Ives Camera as applied to the one reflector or Bennetto’s System. |: is only since the beginning of this century that a real desire ayelq Aug Dry Plate Fig 27.—Light Action in One-Exposure Camera. b The illustration (Fig. 27) “‘ light action in one-exposure camera’ shows how the lens distributes the light rays in a camera. A block ** B C,” has to be inserted to cut off some light rays to protect the horizontal photographic plate from direct exposure to the rays, because the same should receive the light from the mirror “‘ P ” only, even then the peripheric action of the lens may pass some ex- traneous light as indicated by the tangent “E.” If, however, the block ““B C” is made higher, then we are likely to cut off some rays ADDITIVE AND SUBTRACTIVE LIGHT PROJECTION 47 which are necessary to complete the back picture. At the meeting points of the two focussing planes a cut out could be inserted, and must be inserted, if the camera should be used for taking negatives, that is, to fit the camera for the subtractive method. In all Ives’ patents the latter requirement is never alluded to, nor have I any re- collection of a block “‘ B C,”’ being recommended by Ives in any of his two reflector instruments. Fig. 28.—Light action in Chromoscope. The drawing (Fig. 28) “‘ Light action in a Chromoscope ”’ shows that the light rays enter through the glass positives only, and an extraneous light ray “‘ E ” has no disturbing effect on the viewing eye at the ocular, and this is the condition of all the Chromoscopes standing to the name of Ives. After seven years of hard work inventing viewing instruments for the additive method of colour photography, Fred. E. Ives finds Fig. 29.—Photo-chromoscope. F. E. Ives, U.S. patent 635,253, 17 Oct., 1899. that a refraction compensation is required. He has no great opinion of it either, because he files one in U.S.A. only, 635253 on 7th October, 1899. I can trace no English equivalent. The annexed drawing (Fig. 29) shows that only the reflected picture is narrowed 48 COLOUR PHOTOGRAPHY down to bring the same to the size of the refracted picture. The double compensation ‘‘ DC,” and the single compensation “ SC,” can also be inserted at right angles instead of parallel to the mirrors R 1 and R 2, without altering the compensating effect. This, however, is not claimed in the patent specification. The picture in F 3 is twice refracted and twice foreshortened by the reflector filters R 1 and R 2; the picture in F 1 is fore- shortened to the same amount by an inserted plain parallel plate in thickness to the sum of the two reflector filters ; the middle picture in F 2 is once refracted and partly compensated. The compensa- tion is claimed for a three-focus instrument, all pictures being fore- shortened. The tangent “ T ”’ shows that the last focussing plane is exposed to extraneous light, if such an instrument is used as a photographic camera; the apparatus is therefore a viewing instrument pure and simple. Other variations of the apparatus given in the patent specification are more condensed and, therefore, subject to more extraneous light actions in the focussing planes. The patent specification says, as follows :—‘‘ The object of my present invention being to introduce in a reflected image or images a distortion corresponding to that produced in a transmitted image.” Therefore a compensation introduced which does not distort the pictures would be an improvement not claimed by Ives. With such an improvement we deal in another article. COLOUR ENIGMAS 49 SPER XV, COLOUR ENIGMAS printing in colour, to which has to be added all the im- purities incorporated with the colours, the adding of varnishes and other vehicles to hold the more or less transparent pigments of colours, then we shall find the most brilliant blue, yellow or pink will suffer, when the colours are superposed, and that these conditions are the principal reasons, why the top colour, from the three superposed in a colour print, will always impart a pre- dominant hue. The difference between theoretically demanded pigment colours and those in existence, represent metaphorically speaking, an aspect, as, if you superpose in the first case pure transparent glass on a pic- ture, and in the second case, if you superpose more or less finely grounded glass, and if this ground glass were ever so faintly coloured, it would not only degrade the colours in your pictures, but also impart a hue. A similar aspect exists with reference to transparencies. You may look with satisfaction at a transparency made at home, and find it quite right, when viewing the same by daylight ; then when you send the same to an exhibition, the show will be arranged with arti- ficial light of one sort or another, thrown on a reflecting surface, which consists of grey-white, creamy-white, bluish-white or other white paper, and your transparency, which you thought perfect, will show in this transmitted and reflected light a wishy-washy nondescript, degraded in colours, with a predominant hue of some sort. I wish to point this out, because some experts, who judge your work, like to show off, and play on the transparent glass, “ variety, or daylight,” well knowing that it is impossible to attain the object of faultless colour mixture by superposition of the ground-glass variety, especially so if the necessary materials are not yet obtainable com- mercially in any acceptably pure conditions. WW visi we come to look up the possibilities of photographic 50 COLOUR PHOTOGRAPHY When you have come to this understanding of degradations of colours, you will agree with me, that we should not speak of photo- graphy in natural colours, but only of photography in colours, especially so in reference to prints and less so to transparency. The theoretical investigator tells us that a pure blue, a pure yellow and a pure red will form all colour combinations, and that is why we also say “‘ Photography in three colours” or speak about a three-colour print, but, by-the-by, please do not inquire what a pure colour is, the experts are themselves not yet clear on the point, and very likely never will be, yet these colours are to be found somewhere between ‘““B” and “ H ” in the spectrum, having a wave length of 700 to 400 billion ether undulations per second. This statement is made only on hearsay—I never followed such giddy movements. One expert says pink colours are missing in the spectrum, another has his doubts about the yellow, but they all seem to have different shades of “‘ blues.”” The spectrum colours are formed by prism dispersion, and it is a mutable point, whether the prism itself does not deteriorate the spectrum colours, and if a “ grating ” is not more suitable. For us ordinary mortals, who have the inclination to apply everything to handy and practical use, there is no other help than to employ such colours as we can feel, and use them as pigments or as stains of vehicles, because I am positively assured, also on expert opinion, that it would, really be impossible to mix, these phantom colours of the spectrum, with any vehicle and so use them for printing. I have worked the carbon pigment printing process, which to- day is the coarsest ground-glass variety of colour printing on the market, but it is the only process which will give a few necessary prints to satisfy the man of smaller means, who is imbued with the colour-photographic hobby, and it enables him to make some prints to decorate his home with, as proof of his patience, endurance and will-power to overcome obstacles. But the process does not empower him to exploit the same commercially. The subtractive method is at all events something which adds a new power to the application of colour in art and colour printing ; further, if even all the applications are not natural in colours, we shall and do arrive at making artistic pictures and pleasing com- binations in colours, and we do arrive at the point of relieving the monotony of mono-colour prints. COLOUR ENIGMAS SI Allow me also to ask you not to set up chromo-lithographic productions, in which seldom less than twelve litho colour plates are used, as standard or minimum demand, in comparison with colour productions, in which only three colours are employed. There is no doubt that some of the early photochrome pictures show up the colours, showing something of—imagination, and some of the colouring is added in such a way as to give every advantage to the highest pitch of impressionism. We shall never be able to do such things with only three colours; it is absurd on the face of it to demand such exaggerations when limited to three impressions of colours only. §2 COLOUR PHOTOGRAPHY CHAP TER XVit ADDITIVE versus SUBTRACTIVE tive method,” the dividing and assembling of light rays, and the “‘ subtractive method,” by which pigmentary or dye colours are used in forming prints in colours. The scientific teacher has given a special nomenclature to his pet, which in this respect has always been the additive method of colour photography, and so it comes, that the subtractive method has come in for step-fatherly treatment. Primary colours is one of them, the easiest way would have been to speak about additive or theoretical primaries and, sub- tractive or printers’ primaries. The latter were described as primaries by the painters long before the spectroscope showed the possibility, that white light could be separated into colour rays. But no, that would have been too direct. The painter and printer use blue-green, yellow and pink, impossible for them to find a mix- ture of other colours to produce these three colours for him; you think then they are their primary colours. Oh! nothing of the sort, it 1s scientifically proved that blue-green is formed by all the spectrum colours minus orange-red, yellow minus blue-violet, and pink by minus green; the two colours always complement each other to form white together by projection, and it seems that the worker with “ solid ”’ colours sees the blue, yellow and pink only by “ re- flected ” light waves. The additive method of colour photography is the one which in its principles is the fulfilment of the scientific theories and explana- tions of light and colour. The text-books refer generally to it, when they give us their interpretation of primary colours, which seem to be violet, green and orange-red. These colours are best known in their application in the additive working instrument *““ Chromoscope,” and in the semi-additive colour-plate “ Auto- chrom,” and so it comes, that the modern additive worker feels in- clined, and even proclaims himself fully justified, to dictate his additive experiments on the worker with the subtractive method. “Tie principal divisions of colour-photography are the “ addi- ADDITIVE versus SUBTRACTIVE 53 In the additive method you add the colours, not in matter, but in light rays, to form white, and the experience shows, that the filters necessary to obtain the negative colour-records are, as already indicated and specified about twenty years before Ives by Ducos du Hauron and Cros, violet (pink and blue), green (blue and yellow) and scarlet (pink and yellow) and not as generally described as blue, green and red, Ducos du Hauron having obtained his knowledge of the light conditions from the earlier works of Maxwell and others. From the negatives obtained through the above filters, the positives are produced in black and white in the ordinary way, and these positives are in conjunction with the same light filters re- united by projection, and therefore only light rays participate to form the result. The positive made by means of the scarlet filter negative record is projected with a scarlet filter, etc. If now we turn to the subtractive method, we use practically the same filters when using panchromatic plates, as for the additive method, to obtain the negative colour-records ; but the printing by colour material is different. If we add colour matter to colour matter, black will ultimately be produced. The negative obtained through the scarlet filter, also called the orange-red filter, and, if badly described, as the red filter, has to be printed in blue (note the difference from the additive method). The best blue is the shade “cobalt blue.”” The negative obtained through the violet filter is printed in yellow. It must bea yellow that, when mixed with the blue, gives a clear green like filter green, or if the yellow is mixed with the pink a clear scarlet is produced like the orange-red of the filter. The negative obtained through the green filter is printed in red; that is what we aretold. The red, however, is a pink, magenta, crimson, carmine; if this pink is mixed with the yellow the com- bination should be the same as filter scarlet and if this pink is mixed with the cobalt blue the combination should be the same as the violet of the filter. Some experts declare the filter-colours are blue, green and red, and say the negative must be printed with blue, yellow and red. That poor red colour! Anything dark-orange, scarlet, pink, rose-lilac, is called red. It is a marvellously accurate colour descrip- tion and is even employed by some people who fight over one millionth part of spectrum lines, where this or that colour begins or ends in the spectrum. 54 COLOUR PHOTOGRAPHY CHAPTER 2 yy Ha FILTER ARRANGEMENT plate, I have spoken of the reflector filter being orange-red, the back-surface of such plate being surfaced with a medium holding the filter colours. This is a very good filter arrangement, and was specially so at the time when rapid red sensitizers were not known ; it is based on Bennetto’s ideas as given in his patent specifi- cations. This system has, however, a slight drawback, and that is, it allows internal reflections which, when bright subjects are photo- graphed, produce the picture in the top focussing plane with double lines, which are specially noticeable if fully or over-exposed. On the same photographic plate one picture is formed by the direct reflection, and a second picture (if weaker) has its origin in the double refracted reflection. This latter can be killed actinically by using a reflector coloured yellow in the glass mass. This yellow reflector can be surfaced with an orange-red vehicle or a separate coloured compensation (compensation in respect of the filter colour only) plate can be inserted, either parallel with the reflector, or the refraction compensator can hold the filter com- pensation, or this colour compensation plate can be inserted into the dark slide. In this latter case it would, without destroying the effectiveness of the filters, enable the operator to see the picture much better when focussing. This latter arrangement amounts to one fixed and one removable filter. The advantage of a picture cone passing through a filter which is yellow only, is, that the picture at the back focussing plane is nearly as visible as one passed without a colour filter. A green filter is in this respect not so objectionable as an orange-red filter, and when using the latter filter it is sometimes impossible to focus properly, specially so when badly illuminated; and as a rule the focussing has to be done at the top focussing plane. The yellow reflector, coloured in the mass, will absorb the actinic blue-violet light rays, therefore no blue-violet rays from the second or back surface of the reflector filter can be reflected to the top focussing ‘ ), 7 HEN referring to one exposure cameras with one reflector a FILTER ARRANGEMENT 55 surface, where the somewhat diminished, but in no wise altered. light rays from the first reflecting surface, will in this case alone impinge themselves on the photographic plate or plates. A green, that is, a minus red light filter, in place of an orange red reflector filter, has been recommended, in which case the re- flected light has to pass through an orange red filter placed, in front of the focussing plane, before it can be permitted to act on a panchro- matic plate, that is the only place, where in this filter system a minus blue negative colour record can be obtained. The green filter passing blue, green and yellow light acts in this formation on two plates placed face to face at the back focussing plane. First, the blue light will act on an ordinary plate furnishing the yellow negative colour record, and second, will also act on a colour-sensitive plate at the back, which is receiving the minus red light giving the red negative colour record. The top plate in this filter system will require about four to five times as much exposure as the two plates at the back, and under such conditions the one exposure is impossible ; it is then that the loss of light by the reflection can by new means be improved. There is a third filter arrangement, that of using the reflected light to act on an ordinary plate in the top focussing plane, obtaining thereby a yellow negative colour record only. The light transmitted through the yellow reflector filter, that is the light more or less minus blue, according to the density of the yellow filter, falls on two plates on the back focussing plane. The two plates are film to film, the first plate has to be yellow sensitive to furnish the red printing nagative, and the same plate has also to be coloured so as to act as filter; the so filtered light will act on a red sensitive back plate, which latter gives us the blue negative colour record. I find that this filter system permits me to take my three nega- tives with a fairly good colour selection in half the time necessary as when using an orange-red reflector filter. It is always possible to balance the plates in the back focussing plane with the plates in the top focussing plane. With an orange red reflector a plate having a rapidity of 120 is to be used for the front top plate, and a plate of 200 for the back top plate, and now with the yellow reflector filter a single top plate of 200 can be used, that is, this system permits of more rapid exposures. The ‘trans- mitted light is, however, of such a volume that a certain difficulty 56 COLOUR PHOTOGRAPHY exists in finding a good slow plate of the right quality for receiving the light as front plate. Certain dyes embedded in the plate will do that. As for the reflector filter I have taken it for granted that the surface of the glass plate acts as reflecting surface, a surface with a constant reflection and not difficult to keep clean. It has, however, been recommended to silver or platinize the surface to augment the volume of reflected light. This is absurd, for the surfacing will diminish the transmitted light considerably, in fact the metals can be put on so thickly that no light passes, but the metal surface cannot be of less substance as to allow the polishing up. If thinner and varnished an irregular surface is introduced, nor is a varnished sur- face a more brilliant reflecting surface than is furnished by the ordinary glass. If the silvering is applied to the back-surface of the reflector filter we strengthen the secondary picture, etc., etc. Such a remedy gives no reliable and stable conditions to any one-exposure camera system. a a LIGHT FILTERS : THEORETICAL S7 Cle BAMBERG ON HEL Poor il TERS : THEORETICAL. colour screens. To me “ light filters ” seems to be the right term, but colour filters is the term favoured by the expert, and to be correct should have been called ‘‘ coloured filters.” Everyone has seen stained glass interposed into some light tays. For example, red glass in the passage windows, or the dark- room windows of the laboratory. In this one case the transmitted light in the room will be red and seemingly no yellow or blue is passed. A label printed in orange-red or any orange-red object viewed in this orange-red light will appear white and blue will be black, and that is perhaps the reason why some colour-plates are put on the market in boxes having labels in white and red or black and blue, so that you cannot see the contents label on the box, when in the dark-room. This phenomenon represents exactly the position and action of a light filter in a photographic camera, but instead of the human eye, it is the light-sensitive plate at the back of such filters which records the impression. We have to remember, however, that the photographic plate will see only certain lights and only act so far as it is not colour-blind: It is in some way on this colour blindness, that photography in three colours by the subtractive or printing method of colour photography depends. Some photographic plates see only blue, some blue and yellow, some the full length and others only part of the spectrum, and by means of coloured glass or films, we are able to eliminate or render non-recording certain colour rays. We call such a coloured glass a light filter, and the action itself that this light filter performs is called absorbing the colour rays, which action imparts, therefore, an enforced colour blindness to the plate, where the latter without such filter protection would see. For colour photography by the subtractive method we require a blue, a yellow and a carmine-red (pink or rose) printing record according to the density of the colour. (ests filters are also called light filters, light screens and 58 COLOUR PHOTOGRAPHY To obtain the blue printing record, the negative must be covered by the yellow and rose rays, that is, an orange-red filter must be em- ployed, which will pass only its own colours, of which it is composed, that is, from yellow to the ultra-red. If now the plate is a Cyanol plate we can use a lighter and much more yellow filter; if we use a plate of the Pinachrom type, then the filter must be a little darker, and if we use a Cyanin plate then the filter must be dark orange-red, or deep scarlet. To obtain the yellow printing colour record, the blue rays and the rose or red rays, with the exclusion of all yellow, must pass the filter. The latter is therefore of violet-blue colouring. If, however, the sensitive plate does not see yellow, then obviously no filter would be required, and a filter in that case would only retard the light action. Again, if we desire to form a red printing plate, then the res- pective red must be transparent in the negative; blue and yellow must be passed by the filter and both these colour rays must act on the negative, which is done by a green filter. If we use a plate that does not see red, then no filter seems to be required, that is, however, not quite true to practice. The blue rays act always much more than the yellow (or even red) rays, therefore the blue has to be damped down, so that blue and yellow record to about the same density, and we arrive at that by using an adjusted yellow filter ; to add blue to such a filter to make the same green, and therefore more visible and agreeable to the eyes, would be of no consequence what- soever, that is, as I said before, if the plate does not see red, which is the case when a plate is used sensitized with Erythrosine. It is seen by this that if we use three panchromatic plates, then absolutely correct filters are required. If, however, we use three different colour-sensitive plates: a blue-sensitive, a blue and yellow- sensitive and a panchromatic plate, then a much greater latitude in the use of light filters is permitted. Three different colour-sensitive plates is a necessity for one- exposure one-reflector cameras, not only the colour-sensitiveness but also the different rapidity of the plates has to be adjusted for such camera work. In a one-reflector camera, in which the reflector filter is orange- red, the reflected light acts first on an ordinary dry plate, say of 150 rapidity. This dry plate itself acts as a slight light filter, nearly sufficient when using electric light exposures (open arc), yet not LIGHT FILTERS : THEORETICAL 59 strong enough to keep back the blue activity sufficiently by day- light exposure, and has therefore to be coloured yellow. The back plate, which is placed film to film to above plate, is of a rapidity of about 250 and has to be sensitized with Erythrosine. The trans- mitted light acts through the orange-red reflector filter on a pan- chromatic plate, having a rapidity of about 80; thus the three plates are adjusted and receive about the same amount of exposure. I wish to mention here a war-time use of light filters, which were introduced as sight filters. A fluoresceinate or Uranin-coloured gelatine film aids the eyesight wonderfully. Freshly turned earth is at once differentiated, and the slightest flesh tint is enhanced in strength, becoming more visible even though the object is sheltered under the tree. An aeroplane, slightly coloured with this dye, be- comes at once very visible and is as distinguishable as if coloured pink when viewed through a gelatine film stained with crystal-violet. 60 “COLOUR PHOTOGRAPHY CTLA Pat Roa Exe MAKING OF LIGHT FILTERS cameras, but also in three-exposure cameras, so I think it is not out of place to take here both systems under review. When taking three-exposure negatives and we desire to place the light filters near the photographic dry plate we can use ordinary fixed-out dry plates, afterwards coloured, and all three so-made light filters have to be of the same glass thickness. If the exposure is made through a light filter placed near the lens, or if the filter has to act as reflector filter in a one-exposure camera, then parallel plate has to be used and as a whole the com- mercial article called patent plate is quite correct enough when used for light filters. The commercial houses coat these filters by machinery, the colours being mixed with the gelatine before coating, and it is claimed that such filters are absolutely correct, and that bathed filters are bad. This statement is more than one-sided, it is com- mercial embellishment. I myself prepare all my filters, coat the patent plate first with plain gelatine and when dry bathe it to the colour and intensity required or desired. This method permits me to make one filter without waste of material. For separate exposures the filters have to be double plated and cemented. For one exposure the colour film has to be affixed to the back surface of the reflector filter and has to be protected from dampness and injury by a protective varnish; for this a cold- flowing shellac varnish is to be recommended. Certain varnishes and specially celluloid varnish form irregular colour patches. To cover the plates with gelatine, we require measures and a level position. The measure is by preference a spoon holding a certain amount of solution to cover a certain amount of surface. My best results were obtained with a 7 per cent. solution of photo- graphic gelatine, 8 ccs. solution to I00 sq. cm., or one quarter ounce of solution on an English quarter-plate. The level position should be obtained with a plate-glass resting on three points adjusted with (J arnens, bs light filters are not only used in one-exposure OO A a ee MAKING OF LIGHT FILTERS 61 the aid of a spirit level. The room in which the coating is performed should be dust-free and warm ; the warmer the room the more even and glossy the dried gelatine film will be. The warm gelatine solution before coating should be filtered through three or four thicknesses of finest muslin, and all vessels and utensils should be made warm, for which purpose a warm water-bath is advisable. The spoon, when the gelatine solution with its aid is poured on the plate, can assist in spreading the solution, care being taken not to form air-bubbles. When the plates are coated, they are protected from dust with a clean glass cover, leaving an air space between the two plates. A good plan is also to place the whole levelling arrangement in a horizontal cupboard, one end open to let the warm air enter, the other side connected with a flue, into which a small lamp has been placed to create a gentle and constant current of air. For colouring the fixed-out or gelatinized plates very few colours are required ; they must be of the class which colour animal matters, gelatine and wool, and not dyes which colour only cotton. They must also be soluble in water, fast and permanent to light. To ascertain if your dye is right, make a dilute solution, acidify with a little acetic acid, expose one half in a test tube to the sun; if after a few days the colour still corresponds with the other half Kept in the dark, your dye is quite all right. Violet crystals, patent blue, methylene blue, acid yellow or tartrazine, crystal scarlet, fast scarlet, naphthol green, make a good colour selection. The colour solutions, if made from acid dyes, should be slightly acid, 3-5 drops of acetic acid to 100 ccs. solution is about right, and the concentration should be 2:100 if used for double-plated filters, but if used for single-plate filters for one-ex- posure cameras a 3 per cent. solution may be advisable, where such concentration can be obtained. Fast scarlet is mentioned above, and for such I recommend diamond scarlet for wool (also diamond peacock blue and diamond yellow) ; it is an American product easily obtainable in small packets. English scarlets are at present only obtainable by the ton, and only so if you are shareholder of the dye manufacturing company. The orders from an outsider are not accepted, and middlemen looking after the small wants do not exist. Most English scarlets are not permanent. The fast scarlet gives a very good filter and is better than a scarlet bath made by mixing Eosin and yellow. 62 COLOUR PHOTOGRAPHY As a whole mixed dyes will not stain gelatine according to the shade of the mixture; dye testing for this purpose is done by flowing a few drops on plain gelatine-coated plates. Yellow in a mixture stains quicker than the darker dyes, and also when washing a film stained in a mixed colour bath, yellow will wash out before the other dyes. This antagonism of two dyes to colour harmoniously together, or with equal intensity, may explain certain anomalies found when mixtures of different colour sensitizers are used in bathing the bromide plate, where also the characteristics of one sensitizer will dominate over the other. To transform your gelatine plate into a light filter, immerse about ten minutes; if coloured too much the surplus can be washed out. Some colours wash out more quickly than others, so it is advisable to use unmixed colours where possible. But for one example, one plate patent blue and one plate yellow form the best possible double plated green filter, such as cannot be obtained with a combined bath. The gelatine plates when bathed in the colouring bath have to be rocked and moved, so that the colouring matter is absorbed equally by the gelatine, and when sufficiently coloured the filter is washed in a dish or under the tap until all greasiness has disappeared, and the plate is stood up to dry. Ifa film is coloured too much in ten minutes, it would be better to dilute the colour-solution, than to shorten the time of immersion. All colouring should be done at a specific temperature, say 65° Fahr. After fixing out a dry plate and also after colouring a plate, it should be cleared of surface dirt, by very gently rubbing it over with the finest and softest sponge or medically cleaned wool and rinsed before the plate is put up to dry. Double plate filters should be cemented with Canada balsam, the latter and also the plates being slightly warmed. When the balsam is thoroughly liquid a sufficient amount is poured on one plate without forming air bubbles, when the second plate is pressed gently into contact. Clips are then applied to hold the two plates in contact and position till set, when the surplus or oozed-out balsam is cleaned away, for which purpose a rag dipped in paraffin oil will do good service, preventing the stickiness. When cleared of balsam and oil the double-plate filter is bound with a paper edging in the usual way. PLATES FOR ONE-EXPOSURE CAMERAS 63 TAP eRe ox Ne PLATES FOR ONE-EXPOSURE CAMERAS reflector filter to the back focussing plane, the orange red or scarlet filter is attached to the back of this reflector; therefore if we place a red sensitive plate in the focus we obtain a negative, dis- placed about one glass thickness to one corner, but practically in the usual position, just as in any other photographic camera. The negative so obtained is a colour record to be printed in blue. The light filter absorbing a fair amount of light, the exposure will be about 24 times longer than when the exposure is made without the filter, but to balance the three plates for correct exposure, the rapidity of this red sensitive plate at the back is about 80 Watkins, if prepared with Pinachrom or Pinaverdol mixed with one third of Pinacyanol. From the same reflector filter the light, without losing any of its original properties, is reflected to the top focussing plane, but actinically this light has lost about 88 per cent., so that only about one-ninth part of all light that enters the camera is at our disposal to form the colour-records at the top. The first plate at the top is inserted the reverse way, to receive the exposure through its own glass, before it can act on the photo- graphic coating, and we obtain when developed, a negative having its parts in the same position as the negative taken direct by the trans- mitted rays. This bromide plate having a sensibility of about 180 Watkins is an ordinary dry plate, but is made more transparent, having a coating of only two-thirds of the usual thickness. The ordinary plate is only blue sensitive and will furnish a correct colour record for yellow. This same bromide plate, without altering its original blue colour sensitiveness; is also transformed into a light filter ; it is in itself a slight yellow filter, but for our purpose not sufficiently yellow and has to be improved by the following colour bath : For Daylight Exposure: Filter Yellow 1: 1000 Sol.=100 ccs. Water TSOm Pomeriecuic light: Filter Yellow 1: 1000 Sol.= 75" —, Ammonium picrate $ per cent.= 25 ,, Water soa aes ie a one-exposure camera, the light is transmitted through the 64 COLOUR PHOTOGRAPHY An immersion of two minutes stains the plate sufficiently. The plate is then taken out of the bath, and the surplus of liquid swung off the plate, which is then put away to dry. Before inserting this plate in the dark slide, the glass side must be properly cleaned. There are other yellow colours that could be used for the above purpose; to my knowledge no yellow which dissolves easily in water, say with more than half per cent., imparts any colour sensitiveness. Certain yellows reduce, others seem to accelerate, the passing of the light through its gelatine film, and it is the quality of the latter sort which enables me to properly expose a second photographic plate or film, placed in contact, film to film, with the yellow-coloured front plate to obtain the last negative colour record. This last flexible, or preferably solid, plate just mentioned is a gelatine bromide plate of a rapidity of 250 Watkins and has to be sensitized with Erythrosine, the negative colour record so obtained being printed in pink. The Erythrosine plate does not see red, hence no filter to absorb the red is required and the little yellow in the front plate is quite sufficient to damp down the predominant blue actinity. The last negative obtained is a reversed one to the others, and if on a thin support, can be printed from either side. If the negative is required for three-colour carbon printing, it has to be remembered that a flexible plate on celluloid basis is liable to shrink, and is certain to do so in a month or two ; also that a solid plate has to be printed through the back, and if parallel light rays are used for the exposure no material unsharpness will be introduced into the print. In making lantern slides a reversed negative is of undoubted advantage. When exposing the photographic dry-plates in the dark slide, and a flexible plate is being used, the same is pressed in to intimate contact with the front or filter plate with a card followed by a glass plate at the back, and a strong spring attached to the dark slide shutter, should give the necessary pressure from the back. This shows the necessity of single dark slides for one-exposure, one- reflector camera work. COLOUR SENSITIZING 65 ADL Rex: SBOLOUR SENSTPIZING URIOUSLY enough it was the old English gelatine dry (Js existing before Bennett, the watchmaker, of Worthing, discovered by accident the benefit of the warm digestion method, and before Monkhoven recommended the addition of alkalis to the emulsion—these gelatine plates being at that time on the market, and I think Maddox was one such manufacturer—which gave Dr. H. W. Vogel in Berlin the clue to the possibilities of colour sensitizing. In the year 1873, when the wet collodion process was at the height of its popularity, Vogel tried to find out what action the spectrum produced on bromide of silver films, and when examining an English gelatine dry plate he found it had been stained yellow by the manufacturer—obviously for the purpose of preventing in- ternal reflections. He noticed a marked difference of sensibility to the different colour rays, and he forthwith proceeded to investigate the matter to good purpose. The action of Cyanine and Eosine he discovered in 1875, but it was only in 1885 that he published his full researches, made with modern Gelatine Dry Plates, discovered 1878/9. To-day Dr. Koenig, in connection with the Hoechster Farb- werke, has made sensitizing dyes his special study, and when buying these dyes you are informed, that full instructions how to use them are supplied. For colour photography with the one-exposure camera I find that only Erythrosine, Verdol and Cyanol are of utility and a short description how to use them may be welcome here. The original formula was something as follows :— To 500 grammes of distilled water add 15 ccs. 1 : 1000 Erythrosine stock solution and 2 ccs. of ammonia, or 10 ccs. Verdol or Cyanol (or a mixture of these two dyes) stock solution as sold by the makers and I cc. of ammonia. It has been recommended to add potassium carbonate to the sensitizing bath instead of ammonia and 20 ccs. of a I : 1000 potassium carbonate solution can be added o the Verdol solution, instead of the ammonia, with advantage, 66 COLOUR PHOTOGRAPHY but such addition to the Erythrosine bath would be the cause of complete failure. The dry plate is first soaked for one minute in a plain alkaline water bath, the alkali being the same as that of the sensitizer, directly followed by the immersion in the sensitizer for three minutes. The solution must, however, be kept on the move at intervals, or unequal sensitizing will be the result. The plate after sensitizing should be washed in running water for another five minutes, then the surplus is swung off and the plate put up to dry. The above Verdol solution is sufficient for half a dozen half- plates, but not more. The last plate showing about half the colour sensitiveness of the first. The Erythrosine bath can be used much longer, the dye being water soluble. It has also been advised to make up the sensitizing solution with half alcohol and half water. Such an alcoholic bath lowers the rapidity of the plates considerably and the addition of potassium carbonate to an alcohol bath is a positive drawback, also a very questionable help with the Eosines. Cyanol, Pinachrom, Pinaverdol are soluble in alcohol— the stock is a pure alcohol solution—and if added to water, in which they are not soluble, they will slowly be thrown out, forming a sort of colour scum on the border of the porcelain dish when sensitizing. Each successive plate, sensitized in such a bath, can therefore take up only a more and more limited amount of sensitizer, so that no two plates sensitized one after another are alike in colour sensitiveness. It is, therefore, obvious that the addition of a certain amount of alcohol, that is, just such an amount as prevents the above men- tioned throwing out, must be a beneficial one, helping towards a uniform production. By experimenting I found that 15 to 20 per cent. of alcohol is about the right amount to hold the colour sensi- tizing dyes for a sufficient time in solution. This amount of alcohol is also sufficient to accelerate the drying of the bathed plates, and in case of the Eosines as well as of the Cyanins and their derivates helps to give clean plates ; it also saves time. No preliminary bath and no after washing are required. | In a litre of such an alcoholic Verdol bath I have sensitized two dozen 12 by Io inch plates, and on inspection by daylight I found the bath still fully coloured, and looking in a better condition, than the first-named water bath, in which two plates only had been bathed. COLOUR SENSITIZING 67 An alcoholic Erythrosine bath can be used again next day after filtering, but not so the Verdol bath, which is more liable to be decomposed by the organic matter, and as a whole it is the best course to use a freshly-made solution, not using a bath after it has stood longer than two hours, which time is sufficient to form a floating scum or deposit. To impart a proper colour-sensitiveness with an alcoholic Erythrosine bath (or Eosine bath) more ammonia must be used than with a water bath, but with the Cyanines, Verdol, etc., the am- monia can be dispensed with. The advantage is a cleaner and slightly slower plate, which latter, if desirable, can be picked up again by giving the plate an ammoniated fumigation in a special box or cupboard. Ordinary water can be used for the colour bath if no ammonia is added, but ordinary water boiled with a little ammonia and filtered when cold and settled, can always be used. The alcoholic stock solutions of Verdoi and other Cyanines are I : 1000 as sold by the makers. The stock solution for Erythrosine is a two and a half per cent. water solution keeping indefinitely. The sensitizing bath is Stock solution 15 ccs. Alcohol 1508s; Water 820 4, Ammonia (if re- ES pees quired) For colour-sensitizing, pure bromide plates must be used, especially for Erythrosine. Nearly all English dry plate makers add carbonate of ammonia, and such like chemicals to the emulsion before coating, with the belief that the plates will be more rapid and softer working. All such plates are of no use whatsoever to colour workers, who have to, or desire to, sensitize dry plates for colours ; and plates with an acid alum or chrome alum substratum destroy the sensitizing dyes. The plates should be protected from direct dark-room light when sensitizing, and perfect darkness for the preparation of red sensitive plates is advisable. When handling the plates, do not do so by holding the plate up between two fingers, and so allow the saline perspiration from your fingers to mix with the adherent sensitizer and then have the mixture run diagonally over the plate. 68 COLOUR PHOTOGRAPHY The sensitized plates should be dried in absolute darkness and the process should be finished under six hours. It is a well-known fact that colour-sensitized gelatine dry plates will not keep ; if you wish to depend on regular sensitiveness it is advisable to sensitize at home, say once every month, and for that purpose a dust-free dark-room is required, and one which can also be ventilated and warmed. I find there is nothing better for the purpose than a gas stove, one of the box-form cookers, the fumes being carried away by pipes into the chimney, and the free light and air passage below bricked up so that the air is allowed to pass only through a winding passage. The prohibitive price of Alcohol has lately induced me to use Acetone. I find an Acetone bath of twenty-five per cent. much better than an Alcohol one, specially so with the red sensitizers, less so for Eosine which seem to decompose or alter its colour. All plates are perfectly free from scum, even with Cyanol, but a slight overdose of Ammonia makes for fog. It is worth while to investigate further in this direction.* * Dr. Arthur Hubl has shown that whilst some dyes have their sensitiveness augmented by the addition of alcohol, their sensitiveness may be destroyed by using a solution too strong in alcohol. The addition of ammonia, he says, gives a slight gain in sensitiveness provided that not more than one or two drops of ammonia to too cc. of both is used.— Photogr. Chrontk. No. 6, 1920, pp. 41—43. (W.G.) — a ono CORRECT COLOUR REPRODUCTION 69 inte Ree XTi. CORRECT COLOUR REPRODUCTION wrong with the filters as usually described and sold. In a general way we say that an ordinary plate for a yellow record needs no light filter, because such a plate sees only blue. Now I am going to contradict that statement, because my photographic records tell me otherwise. I have found that the ordinary gelatine bromide of silver plate not only sees blue, but also red and certain yellows. I must naturally qualify the reds ; they are specially the Eosine, Erythrosine, Magenta, printing red and similar colours, which are practically missing in the spectrum; in the latter the visible red seems to be similar to our filter red, deep scarlet and orange red, colours which the painter can only obtain by adding yellow to the just mentioned Eosine colours. Now all these orange-like colours, these spectrum reds, will not record in the negative, they will show the same as yellow, that is, will be transparent in the negative. On the other hand all the reds minus yellow, the Eosine series, will record exactly like blue, that is, show opaque in the negative. For my explanation I classify the yellows into “ ordinary ” and ‘‘ special” yellows. To the latter belong all those which do not cut from the violet, but from the yellow green end of the spectrum, and these, when photographed by an ordinary plate, return a record just like the blue. See No. 1, Fig. 30. This defect is not eliminated when using a blue-violet light filter in conjunction with a panchromatic plate. But this special yellow can be made to record correctly in the ordinary bromide of silver plate by inserting in the light path a light yellow filter. I use an isochromatic patent plate as sold on the market. The second negative colour record, taken on an Erythrosine sensitized plate, is supposed to see yellow and blue only. This statement is not quite correct, because such a plate sees all colours except filter red (spectrum-red, scarlet and deep orange). Yellow green also is not recorded so well as blue green. To make this [wrens are times when I feel as though something were 70 COLOUR PHOTOGRAPHY Erythrosine plate serviceable, I require a yellowish light filter, a filter whlch slightly cuts down the blue activity in the violet end of the spectrum, when the Eosine series will become more transparent in the negative ; therefore the printing qualities will be improved, because the printing red, the red minus yellow in the red colour record can now be printed. If a red negative printing record is to be obtained, by means of a panchromatic plate, the light filter has to be green, Naphthol green in preference. A filter minus red must also cut out the extreme violet. If violet is of the same density as blue, as many green filters permit of, how will you obtain a violet in your print without the necessary red ? Now we come to the third negative colour record, the blue printer, for which we use an orange red filter in conjunction with a panchromatic plate. As a rule the filter is too dark, so that blue and green are rendered alike in the negative. The red sensitiveness in the modern panchromatic plate is such that violet and the Magenta colours are recorded of the same density as Eosine or orange. This negative has to be printed in blue and if for violet and magenta the blue forming part of such colours is opaque in the negative, how will you obtain these colours ? For that very reason I prefer a Pinachrom or Pinaverdol plate if a very rapid exposure is not required, because such a plate would not so quickly be over-exposed in the extreme ends of the spectrum and therefore leave violet and magenta more transparent in the negative record. 7 All the experiments refer to exposures by daylight. The negatives so obtained are of a mellow appearance, whereas artificial lights are apt to render the same somewhat harsher and cleaner, through under-exposure in the shadows. I have found an artificial spectroscope of great help. It is formed of a series of coloured gelatine films. These are dyed with Violet crystals, Methylene blue, Patent blue, Acid-green, Naphthol green, Acid yellow, Uranin, Filter red, Eosine, Xylen red ; the latter could be replaced by Fuchsin. The effect of an exposure without a filter on an ordinary plate is shown in the first record in Fig. 30; a like result is obtained with a crystal violet filter. An acid green filter, a signal green glass or a light isochromatic screen cuts out more of the yellow as shown in the second record. CORRECT COLOUR REPRODUCTION 7! 1. Ordinary plate. No filter. 2. Ordinary plate. Iso filter. 3.Erythrosin plate. No filter. 4. Erythosin plate. Signal glass. 5. Erythrosin plate. Iso ffter. 6. Erythrosin plate. Naphthol green filter. 7. Cyanol plate. Orange filter. 8. Cyanol plate. Orange filter. ‘ Fig. 30. 72 COLOUR PHOTOGRAPHY With a methylene blue or patent blue filter a result is obtained some- what between the two. It is also worth knowing that when interposing a yellow green or naphthol green filter into the light cone impinging on an ordinary plate the four top fields only would be exposed. Speaking now of an Erythrosine plate and exposing such to direct light without the interposition of a filter, the result will be like the third record, all colours registering with the exception of the orange red. A crystal violet filter will give a good yellow colour record similar to picture 2. The yellow record is less pronounced if ex- posed through a patent blue filter, and a signal green depresses the Eosine too much, to the detriment of the yellow as shown in the fourth picture. The fifth record shows the effect of a light Iso filter, and giving as good a colour record for red as could be desired. A yellow- green glass or a naphthol-green filter of middle density gives a some- what exaggerated red printing record, showing that a light naphthol- green filter is a quite sufficient filter if used with such a plate. The last two records are made by exposing a Cyanol plate through an orange filter. If pure Cyanol is used the plate pre- disposes greatly to solarization in the red high lights, whereas a Cyanol-Pinaverdol plate is free from that defect if no ammonia is used. | If a slight loss of light is of no account then a Pinaverdol plate is much to be preferred ; such a plate will correctly record the blue tint in the field next to the neutral tint, while the Cyanol plate produces the same result as Eosine. A Pinaverdol plate obtained without ammonia in the sensi- tizing bath is very slow; the sensitiveness is increased about five times with ammonia, when it will be about two-thirds that of a Cyanol plate, the latter being sensitized without ammonia. The last record shows the effect of under-exposure. It amounts practically to a false colour rendering, a thing that can be obtained with the best of plates and filters and shows the value of standar- dization, the necessity for the operator to know his light, plates and filters. . The search for “ absolute” filters with which any so-called panchromatic plates will give perfect results in the hands of a me- chanical worker cannot be complied with. They do not exist, and the £1,000 offer for such is only an invitation to be swindled. BALANCING OF FILTER AND PLATES 73 CHAP DER XXIIT. BALANCING OF FILTERS AND PLATES E have in aniline dyes the means to filter out some lights. W\ Generally speaking the light that passes the light filter, and reaches the eye, will in the major part also prove to be the active part of the light passed. The rays that will not pass through the filter cannot act on the plate, and the plate will show this imparted colour blindness as printing quality. Generally speaking, if in a light filter certain colour rays, which we desire recorded on a photographic plate, cannot pass, we have to augment that colour in the filter; or if the filter is already too denise, we have to diminish the predominant colour. Further, if the colour-sensitiveness of the photographic plate is less in one part of the spectrum than in another part, for one colour than for another, we can partly correct this depression or gap, by passing more com- pensating light rays of that respective colour through the filter. I mentioned before that the printing quality is the principal thing for us, whereas just the opposite qualities form the principal requirements for the transparency or additive method. The reason , is because in this latter, we take with a blue-violet filter a negative, which records the blue-violet colour rendering by opacity, and this in the glass positive will therefore become transparent, so that when projected by the aid of a blue-violet filter it will show blue violet ; the same applies to the green and orange-red records. — But for the printing or subtractive method, the negative for the blue record is obtained through the orange-red filter—a filter minus blue. The green filter negative gives the pink records and the violet blue absorbs all yellow to enable a yellow print to be made.. In my illustration (Fig. 31), I try to show the relative action be- tween plate and filter in reference to the subtractive method. We must also keep in mind, that if the colouring of the filter is too weak, not enough undesirable light rays are cut out, and the print will not show the full density of the colours desired. A similar defective colour effect would be produced by the want of contrast in the negative. 74 COLOUR PHOTOGRAPHY 400 430 490 535 590 660 690 vie ' Blue ‘Gr iYellow' Orange. Red ' ‘ Blue filter. Ordinary plate. Negative. Yellow print. Yellow filter. Erythrosin plate. Negative. Red print. Yellow filter. Orthochrome plate. Negative. Red print. Green filter. Erythrosin plate. Negative. Red print. Orange filter Pinachrome plate. Negative. Blue print. Orange filter. Cyanol plate. Negative. Blue print Yellow print. Red print Blue print. BALANCING OF FILTER AND PLATES 75 My illustration shows in each of the different sections, the absorption of a filter, the photographic plate and its colour sensitive- ness, the negative recorded, and the print obtained. The filter shows the absorption; the plate, the colour blindness; the negative, the transparent parts ; and the print the residue as printing quality ; all indicated by the dark spacings. Section “a” shows the action of a blue filter on an ordinary dry plate, which latter is also called the blue plate, being sensitive to the blue rays only. This blue sensitiveness is relative only, because with any other filter and much longer exposure, any other negative colour record could be obtained with it. A violet filter would pass a little more red, which would show when using a panchromatic plate. The different sections, b, c, d, e, f, g, explain themselves ; the last section shows the three colour selections required for three- colour printing. We are told by some authorities that with a spectroscope it is a perfectly easy matter to adjust all filters, and that without such a costly apparatus we are unable to find the proper filters and plates. Such a dictum I cannot accept as I have tried different means— means that were already indicated by an earlier worker, A. von Hubl. Moreover, a complete spectroscopic, or, in other words, theoretic adjustment is to my idea not possible when using one- reflector cameras ; we can only use a practical adjustment. To adjust all filters and harmonize them with the plates, I re- commend the use of a colour chart, such as can easily be made with Methylene blue, Patent blue, Naphthol green, Acid-yellow, Uranin, Orange-yellow and Filter red and Pink ; or again the colour printers’ standard colours can be used for the same purpose. White paper must be used as support and colour must be applied to saturation. If some dead black, platinum-grey and white are also represented in the chart, then we are every bit as well equipped, and it is also cheaper than using a spectroscope. We simply photograph this chart and the resulting negative will reveal all.we desire to know. This shows the necessity of harmonising plates and filters together. The best of filters used with a wrong or unsuitable plate may not give the result you require, so “ verify ” and don’t accuse others with your own want of understanding. 76 COLOUR PHOTOGRAPHY CHAPTER? XociNs EXPOSURE. we have only an ordinary photographic camera with three single dark slides to experiment with, and we desire to use this camera for such a purpose, then we charge one slide with the blue filter, and an ordinary gelatine dry plate, which is blue-violet sensitive only, in preference ; in the second slide we place a light green or light yellow filter and an Erythrosine plate and in the third slide a scarlet filter and a panchromatic plate. The light filter must be clean and dust-free and, by preference, should have the film side facing the subsequent exposure; the filter will then be less likely to be injured and small defects in the same will then not be too sharply reproduced in the negative. To keep the plates in position packing has to be introduced. If double slides are used the partition - has to be removed, so that they can be used as single slides, and the side on which the exposure is to be made, must be specially indicated. Before we are ready to expose the plates, we have to adjust the focussing plane, accounting for the compensating distance of the thickness the light filter displaces the photographic dry plate. For my own use I had constructed three slides, which allow the insertion of the light filters from one side, and the dry plate from the other side, having a separation between the two of 4 centimetre. The slides carry outside also a small coloured insertion of the same colour as the filter inside, a precaution which gives me sure information of the contents. I also took care to cut out one notch in the separation containing the green filter, and two notches in the separation containing the scarlet filter, which notches will be self-registering on the exposed plate, and effectually prevent the negative colour records being afterwards mistaken. Before we start on our regular work, we have to ascertain the exposure ratio of filters and plates together, and for this purpose we expose a set of plates on a colour chart, as indicated on page 70 and 75 and the negatives so obtained should show white, ae gain our first knowledge of colour photography, suppose EXPOSURE 77 platinum-grey and black in all three records alike ; only the colours should be recorded differently. For example, my filters and plates work at the following ratio : Lumiere blue label plate with light-blue filter one and a half; the same Lumiere plate sensitized with Erythrosine and used with a light green-yellow filter two and a half, and the same Lumiere plate prepared with Pinachrom and the scarlet filter ten, or only five if sensitized with Cyanol. The time of exposure I find easiest with the assistance of a Watkin’s Bee-meter, the time required in exposing the same to the dark standard being about the same, as required for the Pinachrom plate with a lens aperture of f/10. If making exposures for colour work, it is essential that we do so only, when good light is available, because the actinity of the red rays in dull light diminishes more rapidly than the actinity of the blue rays, a point which has to be considered, when exposing with three-exposure cameras. In one-exposure cameras there are reflec- tors, we cannot do without them, and the reflected light also loses its actinity quicker in dull light, so that to all appearances a one- exposure camera which makes use of the reflected blue actinity has the different light actinities always more equally balanced for all three requirements to form three properly exposed negative colour records. Fig. 32.—Change of light in day-time. Suppose now we find a subject for a three-colour photograph, a view of a cross road in which there is a wall parting light and shadow (Fig. 32). If now the exposure ratio for the scarlet filter would be five minutes, we should require another five minutes to change and expose the other two slides ; say in all ten minutes are required to expose three plates with a three-exposure Camera, a time which the one-exposure camera could do in five minutes all told, with the same light and stop conditions. 78 COLOUR PHOTOGRAPHY How this time allowance of ten minutes slips away, let me illustrate by the following. The travel made by the sun in twenty- four hours has been divided into 360 degrees, from which we can calculate 15 degrees in one hour or 2} degrees in ten minutes. If under these circumstances the shadow or light has an effectual distance of 50 metres, that is, from one object (the wall) on one side of the road to another object (the scales) on the other side of the same road, then our sunshine would travel at the rate of about 50 metres in four hours or full 2 metres in ten minutes, and that would be during the ten minutes required to photograph a view. This “ change of light in daytime ” on the opposite side of the road, we can also calculate as being 4 centimetres at a distance of I metre, or I inch at a distance of 25 inches during ten minutes. This change in shadow and light must, of course, reveal itself in the finished three-colour print, and it does so by showing itself as colour fringes. It will show itself in the most obnoxious way when photo- graphing moving subjects. If we take, on the other hand, the same subject with a cne- exposure camera, these colour fringes cannot form, because the change of light is registered alike in all three negatives. If, during exposure on a landscape, the light changed partly, it would materially affect the three exposures, but never the one exposure. Only fancy the following case with three exposures, one negative is obtained with full sunlight, the second negative with the sun partly behind a cloud, the third negative with a slight smoke from a locomotive passing through the landscape, or only the smoke from a chimney top changing its direction. I am sure it would not be the operator taking such things who would suffer the penalty, but the poor printer, who relied on conscientious work from his predecessor. If we take an object for the value of its colours, we must see that the object is well lighted. If, for example, flowers or a short- distanced view is the object, then I advise subdued light, or if sun- light has to be used, then do not take the photograph when the sun is high, but at such a time when a minimum of shadows are created, and have the light strike the object nearly from the front, as nearly as possible in the same direction as you are posed towards the view. It is not the shadows you photograph as in an ordinary monochrome photograph, but the best reflections of colour from your coloured objects. EXPOSURE 79 In judging the colour effect on your object look at it with one eye only, and that one eye shut to such an extent as to produce a diaphragm effect with the eyelids. You soon will find, in looking at the object, whether you have enough colour left to predominate over the effects of shadows, dark non-coloured objects and the reflex lights, and you can then draw your own conclusions as to fitness for a photograph in colours. We often look at a tree and may see only a few green spots, but because we know that the tree is green, we imagine we see the whole tree as green, at the same time the tree might be one mass of shadows, so that its colours would really be represented by black; therefore, remember the camera would more than differentiate the colour effect. 80 COLOUR PHOTOGRAPHY CHAPTER XXV. LABORATORY which the temperature should always be the same, say 65°F., so that the work can always be depended on. The development of colour negatives can only be carried out in darkness, and the lifting of the plate out of the developer, and inspect- ing the same by transparency, in front of the ruby glass, has to be discarded absolutely. The development has now to be done by time, and the time factor depends on the temperature. Nearly every kind of developer is serviceable, with the exception of ammoniacal solutions, but the Amidol developer is very good, when made from fresh and white powder; this developer has the tendency already to discolour when dry. I myself have been perfectly satisfied with the following developer : Dissolve in 700 grammes Hot water. 3 Re Metol. 3 oe Hydrochinone. 20 ce Soda sulphite anhydr. 100 os Soda carbonate, pure. I fn Potass. bromide. Store this stock solution in small bottles, holding say 25, 50 or 7O ccs. equivalent to I, 2 or 3 ounces; when full and properly corked it will keep any time, and for use it should be diluted with the same amount of water, the bottle being the convenient measure for the same. When developing three colour negatives, taken with the one- exposure camera, having one reflector filter, it is to be remembered that one plate is reversed, and has to be placed the film uppermost into the dish. The operator must take care to know which plate he is developing, as this has to be done in the dark, because the different plates require different time. The blue or panchromatic plate, exposed through the scarlet filter, takes two and a half minutes to develop; the yellow or ordinary plate, receiving the first reflected ‘ colour photographer has to have a proper laboratory in LABORATORY SI light, takes three and a half minutes and the red or Erythrosine plate takes five to seven minutes to develop. When properly fixed and washed they are surface cleaned with a swab of cotton and stored up to dry. Ifthe Erythrosine plate is a flexible one, care has to be exercised that the drying is done slowly and equally without distorting the same. It is sometimes necessary to intensify negatives ; for this pur- pose immerse the dry negative for a few seconds in plain water and then bleach in a solution made up of equal quantities of one per cent. potassium bichromate and half per cent. acid hydrochloric. After washing in semi-darkness, expose to light, diffused daylight in pre- ference, for a short time, and re-develop with the ordinary developer till fully black. When reducing a negative an agent must be employed which does not eat away the half tints, and for that purpose I strongly recommend the following : Red prussiate, freshly made 3% = I00 ccs. Soda carbonate stock Se On, =e lOne,, Minmouitmienitrate stock .. 10% = 10 -,, femlomde.0f sodium stock... 10% = 10 ,, Immerse 10, 20 or 40 seconds, rinse and fix in fresh hypo. ; if not reduced enough, repeat the operation, but always rinse between each change, never work with stagnant solutions, or unequal reduc- tion will be the punishment meted out to the careless worker. The negatives should show a fine and complete graduation, the densest parts, which represent white, or reflections should just miss being transparent. Dense negatives are no good, they give a false colour rendering, because parts that should show slight colour- ing are not allowed to act when printed and negatives which are too contrasty obliterate all details in the shadows. If you desire to clear your negatives of the white deposits from soda and carbonates showing after fixing, wash slightly and then pass the negative through a water bath to which has been added a few drops of acid acetic. Metabisulphite is for the extravagant. Safelights are recommended for colour workers, but a safelight is a myth if some light rays pass through it, and if no light rays can pass, it is absolute darkness. It is, however, possible to relieve the absolute darkness with the comfort of some light, and this “ dark- room illumination ”’ can be managed as follows. Asmall oil lamp or 82 7 COLOUR PHOTOGRAPHY quite small electric lamp “‘ L ” (Fig. 33) is placed in such a manner in a lantern, which has an ordinary ruby glass, that the light is thrown along a lower bench only towards and into a box “ B,” having an opening which stands a short distance away. The light rays are swallowed up in the box and the top “‘ T ” forms a second bench, which is in absolute darkness and where the plates Fig. 33.—Dark-room illumination. can be handled with perfect security, so long as they are not exposed to the light. My lower bench can hold the watch, developer or chemicals. This little light is just sufficient to keep us'in touch with the pleasures of life, one feels not altogether buried. To be doubly sure of the illumination, a swinging shutter “P” with a smail box attachment can be fixed to the lantern front, and when shut down an opening ‘“‘ S ” under the small attachment could still illuminate the watch. Development is, and will remain, a mechani- cal operation performed under controlled conditions. I wonder if a surface prepared with luminous paint would give a sufficient and safe dark-room illumination for handling panchro- matic and other photographic plates. I may here add a hygienic hint respecting chemical eczema to which some people are subject through handling chemical solutions. Wash the hands often in warm water, using soap, then replace by chemical action the abstracted fat with an ointment made of lanoline mixed with a minimum of glycerine and castor oil; this is the best remidy I know. Velvety skin is the sign of health. Eczema starts with a glossy skin, having the appearance of a more or less horny collodion film. CAMERA CONSTRUCTION 83 iA Pal Rox Vil, CAMERA CONSTRUCTION. FEW years ago a cyclopedist of all trades, but with special A tecorstia photographic proclivities ventured to describe how to build a one-exposure camera, and most accurate results were figured out. Now, if square areas have to be made to measurement, such can be fairly and accurately obtained ; not so if reflecting surfaces at an angle and of uncertain thickness come into play. Such measurement may theoretically be reckoned out, but the constructor is unable to follow such directions accurately, and therefore to furnish an instrument optically correct other means have to be used to attain that end. For a one-reflector camera a bed is required to hold the re- flector in its-place, and such bed has to be most accurately placed; I think this is the most important item to attend to, being the place where the refracted and the reflected light cones are balanced. Space has also to be given for the compensation plate and the thickness of _the two glasses has to be accounted for. The horizontal and vertical size of the focussing planes as to size of plate and length of the optical light-cone has some bearing in the construction of the camera, which must have absolutely secure, adjusted and permanently fixed focussing planes. No collapsible contraptions are possible, such outside specialities are only for the gullibles and for such pretenders to wisdom who do not work the instrument, but know everything else about it. The best way to make a one reflector camera is, with the help of a ‘“‘ constructive guide” (Fig. 34), to make a solid guide and use such. Say we will make such a camera for plates 3} by 44, then 34 plus 44 is 74, which is the length of the central ray “‘ C ” passing to Fi, the inner focussing plane forming part of the light cone coming from the optical centre. If now we erect a line at “‘ K ” slanting at 50 degrees, this line will cross the exterior upper light ray at “‘ L;” from that crossing point we form at the same angle another line ‘““L” to “B.” This Riese Dor. B’- Mis the bed. “P= for the: -re- flector; in such a camera ‘‘ L’’-“‘ K,” if extended to “‘ G,” shows 84 COLOUR PHOTOGRAPHY the direction in which the compensation has to be laid down. If now we cut out a solid tin or brass plate “B”-“E”-“D”- ‘“M ” and we file into it one or two registering marks “ H ” into i Z Fig. 34.—Constructive guide. the bed-line “‘ B”—“‘M” we have a complete “ constructive guide ’ for making our camera, especially if our compensator line ** Co ” is also indicated on the same Ries sisi sisi di ll NAS re a 50° . ~e~—eM Mg Mg Bg Me Me wer Ke eM Me ew ewe ee eH em ewe ee ee ee Fig. 35. Construction of One-Reflector Camera with Compensation. Referring to Fig. 35, “‘ Construction of one-reflector camera with compensation,” we start by squaring up the ground floor of our camera, inner width 4} and length 63, and then flank the same CAMERA CONSTRUCTION 85 with two side-walls, inner width 63 by 63 length (plus joining up wood) ; when fixed lay down your “ Constructive guide ”’ on a side wall inside, square up with “‘ B-E-D.” Adjoining the constructive guide fix a temporary block, leaving an opening near the registers “H,” then fix a metal blade “‘ BE” upright into the side wall so that it projects beyond “ P,” see that “‘ B-E ” is perfectly level with the ground and that the upright is adjusted to “‘ E-D ” the back- focus F 2. Also allow for one glass thickness which corresponds with the displacement of the picture plane caused by the refraction through the two glasses. The next step is to remove the constructive guide, and to fix a strong squared bed-support from the bottom to the top, flush against the temporary block, having first cut out an opening, so that the two metal blades are not interfered with. If the bed-support is properly fixed with glue and screws, the temporary block is removed, and the construction guide is put into its place, making use of the two metal blades and the fixed bed support, when the top focussing plane “‘ T”’ is found. The focus should, however, be displaced to ‘“< T-F,” half a glass thickness or so, to leave room for a finer ad- justment later on. It is to this latter distance that the side wall has to be planed down; the other side wall is treated exactly the same and both are then connected up to finish the camera. If the displacement of the picture plane has not been accounted for at the back focussing plane, the central ray can be marked on the top focussing plane as one thickness of the reflector towards the lens board. The focussing planes here given are the rests for the dark slides, and must on no account be further altered. The reflected focus is also just a shade longer, so that we are able to adjust the two focussing planes with packings on the bed support. Two points of packing force the top focussing plane three points further away so as to be in register with the back focussing plane. If we have marked a perpendicular line from “M” to “Z” on one side wall we have the place for an upright bed support which we fix innermost, then we connect the line with “ G”’ on the dia- gram of constructive guide of the opposite corner which gives us the guide for the compensation plate. This plate has the corner cut off near ‘‘ M ” so as to be able to go into its place, which is at the back of the reflector ; the latter is slanting from bottom to the top, the compensation plate is slanting from one side to the other. 86 COLOUR PHOTOGRAPHY Before fixing on the guides for the slides in their respective places, the front for holding the reversible, or other, lens board has to be affixed. It is also advisable to insert a solid transfer piece from ‘“N ” to the top, connecting the side walls, to give the camera box perfect rigidity, and also to exclude extraneous light from passing over the reflector filter to the back or to the top focussing planes. R set § O80 « . Laoey ° SARE oes reat . * ; F ° Fig. 36.—Constructive block The compensation can, if desired, instead of after the refraction, be inserted (as D-C Fig. 29) parallel with the reflector into the re- flected light-cone (as patented by Ives in the United States of America for his two-reflector system only) in which case all pictures will be slightly distorted; also, internally reflected rays may cause some trouble, and may be the part origin of what Ives declares to be ** polarized light effects.” If this latter is not entirely due to ex- traneous light rays, as we have seen, none of his cameras, taking negatives, are protected from such light infiltrations, and as no such protection is indicated in any of his patent specifications. No such references came to my view. Fig. 37.—Last. There is a second way to build a one-reflector camera, and that is with blocks used as last. The constructive block (Fig. 36) sawn into two parts on the line “ P ” will form a “ last ” as shown in the drawing (Fig. 37.) The proportions are the same as with the constructive guide. Fi and F2 are the focussing planes, the lens board “‘ O ” must be erected square at “‘ B ” on the line “‘B-D.’’ VERIFYING THE FOCUS 87 CRAPT ER “XXvit; PenIPYING THE FOCUS approached with a view to taking an interest in one-exposure camera work, have declared that it is impossible to make three negatives of the same size when taken in more than one focussing plane and about half of the above number were sure that the red printing negatives would be out of size. Now as the red negative record is always obtained with one of the others, film to film in con- tact, how can it be of a different size from the one with which it is taken? That seems obvious, but the engraver is absolutely positive that it cannot be so. How does he come to that knowledge ? How does he verify ? He simply superposes the glass positives and there you have the complete method! He does not trouble about the inter- vening glass thickness. This is all so primitive that I cannot help being sarcastic about it, and all said and done, it is a startlingly mis- leading way for an expert (which they all claim to be) to condemn other people’s work, submitted in good faith, and trusting to honour- able treatment. Others, when making the glass positives, never thought that in reversing one of the negatives, they themselves, by omitting to add the compensation of the glass thickness, were making glass positives of unequal size from equal sized negatives. For this they did not blame themselves, but only the man with the one- exposure camera. These few words must give me the excuse for explaining how the experimenter should go to work. First, a large white sheet is placed at a certain distance before the camera, but so that the sheet is about at right angles to the central ray of the lens. The enlarged plate size is then marked on the sheet, then just inside the enlarged plate size two or three thick and two or three thin, black, horizontal, vertical and diagonal lines are drawn. These lines are then photographed, first on one plate in the back focussing plane and secondly through a blank and trans- parent, but slightly marked front top-plate on a second plate in the top focussing plane. Thus, we have one right-faced and one reversed negative, which when placed face to face and superposed, have no GQ pooroacies like fifty per cent. of the engravers who were 88 COLOUR PHOTOGRAPHY glass separation between them, and will give the best possible in- formation about size. If the marked top plate is too large, then the reflecting distance has to be diminished, which can easily be done by placing some packing under the reflector filter on the reflector rest. The packing is best made with wood shavings which are fixed with glue to the rest. Very small differences can be adjusted with paper, but the same has to be of a solid and pressed kind. When once the two focussing planes are adjusted, they are for all intents and purposes permanently so, but occasionally require verification like everything else. A difference in size of 3 mm., through the top registering longer, has to be adjusted with 2 mm. packing. Ordinary or enlarged glass positives of any subject as derived from the daily work can best be verified by making a contact print on glass from one of the three glass positives. When dry it must superpose on all three glass positives. The result is better visible if the contact print is converted into a colour print, say a blue Cyan print or Uranotype. The original negative can be verified by printing a glass positive from the reversed negative, and superposing it on the other two negatives. These are the proper ways and means of honest verification. One of my critics used a toned bromide print and two superposed carbon prints, the paper supports stretching different ways, and yet blamed the glass negatives for being out of register. The colour correctness of the results gives another ground for criticism. Here is how it is applied :-— One of the great process houses in town had to make a block print of one of my views for a publisher, and when the three colours were superposed, it represented a completely black smudge; even the sky was black, and yet when each negative was printed in the ordinary way on P.O.P., all the details and graduations as demanded of a good photograph were present as a sure guide for the engraver and the photographer. I take it that the engraver did not expose his screen negatives correctly, or did not etch the copper plate properly, or used a badly cleaned roller for rolling up delicate colours. May I be permitted to ask, did he know his technique, did he exercise his proper skill, or did he do such foolish work for a motive ? I may add he was paid for the work. Needless to say the publisher was convinced that the one- exposure man was a swindler of the first water. The amenities of a specialising worker. VERIFYING THE FOCUS 89 One-exposure camera work should not be difficult for the process man to adapt, even if there is no colour picture as a guide, because there are, nevertheless, in every three-colour negative certain indications recorded, which help to prove that the negatives or posi- tives can be read for colour values. High-lights and light subjects should surely be rendered as such in the block, and blacks and deep shadows give the other extreme; and to my mind colour subjects are better rendered if the extreme shadows are weak, than when the high-lights are over-printed, but to make a black print with three colours is absurd. 90 COLOUR PHOTOGRAPHY CHAPTER XXVIII. PROCESS “FAKING graduated. The high-lights, reflex lights and whites which are exposed directly to white light must show full density in the negatives; by full density I mean, just so dense that in a P.O.P. printing exposure of ten minutes in good light no appreciable discoloration takes place. Further, the most transparent parts in the same negative representing the deep shadows and black objects should print at the same time to a good black without, what the professional calls, turning bronze. If we make glass positives from the negatives, either by contact printing or by light projection, they should show the exact opposite. If we under-expose and over-develop, we stretch the scale of gradua- tion and lose some of the middle tints, by merging the latter into the high-lights and shadows. If we over-expose and over-develop we add extraneous colour values, we alter the area of the deep shadows and flatten out the remaining scales of half tints. Thin positives favour over-crowded process blocks, dense positives suppress the fine middle tints and are the first cause of destroyed colour values. The positives can be retouched, in some cases it is even ad- visable. A small wash with aniline dye will sufficiently intensify certain colour renderings, for example: We take a straw hat, always as being yellowish, but actually in the original the colour is a very feeble cream and hardly differentiated from white. To gain the popular approval a little intensification on the yellow positive record would greatly improve the colour. Then there is that gap in the green, a wash in the corresponding parts in the red negative record or over the yellow positive record would greatly improve the colour rendering without destroyjng the half tints. When the process man receives the glass positives he has first to make screen negatives ; naturally here also a good man can do good or negligent work just in accordance with his applied know- ledge, skill and understanding of the requirements. NU ceases. taken for three-colour work should be well PROCESS FAKING OI No reversing prism or mirror is necessary when a negative in the correct position is to be made from a glass positive, and the illumination should be made in the orthodox way by reflected or by filtered and dispersed light; the exposure through transparencies should never be made by direct arc light, which cuts up all half tints and reduces all high-lights to flat fields. Asamethod this is favoured by the operator when he is pressed for time. He does not like working with glass positives, because he has to alter his camera position, and attend to other little things which are not in his daily routine. When, with the aid of the screen, the continuous half tints of the original are transformed photographically into dots, it is perfectly easy to expose so, that the dots representing the middle tints are over or under-exposed. The negatives can be made so that the dots are too much or not sufficiently joined up in the high-lights. The dots in any negative can be made larger or smaller, a larger dot meaning a darker picture and a smaller dot a lighter picture. When the screen negative obtained is printed on the chromated metal destined for the block, the process man can make further mis- takes in etching too much or not enough. Besides, it is an understood thing, that all former mistakes can be rectified by a fine etcher, which is often the official title for “‘ faker.” This admirable person is really unable to work without a colour original and is specially fond of correcting the red plate, and fine homogeneous patches he makes of it, faking out all details; parts of these doctored pictures have in this way lost their rotundity. 92 COLOUR PHOTOGRAPHY CHAP RE RX DIAPOSITIVES OR collotype three reversed negatives are required, and for | eee a process the plates on which the negatives are obtained can be inserted in such a manner that two negatives are taken one way on glass plates and the third negative is taken the other way. This Jatter is taken on glass or celluloid, but both have to be printed through the back. The slight unsharpness introduced when glass is used is very small, specially so if printed in direct and not by dispersed light. It is not advisable to use celluloid for larger plates, as such a negative is inclined to deformation, through shrinkage and unequal dessication or through hygroscopic influences. A new collotype-like process was suggested by Handel Lucas, in which bromide prints are treated as in the bromoil method, and coloured up with fatty inks in colours. The inventor claimed to be able to print a thousand prints from a prepared bromide print by means of a resilient transferring pad. This very promising process has been killed in its infancy. At present it is only three-colour printing from process blocks which offers the means for book illustrations, though I am told that when the half-tone method is employed in conjunction with the offset. press any number of prints of great equality can be taken off. If colour record positives are required for block making, then paper positives, which are generally called “ prints,” are of ques- tionable service. The paper may stretch unequally when it has to go through the different photographic processes, so on the whole, it is best to supply positives on glass, also called diapositives, to the photo-engraver. Three-colour negatives taken with the one-exposure camera have no grain, when compared with screen colour plates, one-plate colour transparencies or Autochromes, and can therefore without detriment be enlarged five and more times the original negative size. When making glass positives I find the ordinary slow speed bromide of silver plate good for the purpose, though I prefer wet collodion plates. DIAPOSITIVES 93 Two right-sided and one reversed negative are supplied by the one-exposure camera, and we have to redress the reversed negative when copying for the above purpose. Certain precautions have also to be taken, so that all negatives are placed at the same focussing distance in the enlarger or copying apparatus. We have in fact to account for a difference of a glass thickness. The three negatives should be on glass of the same thickness and the copying must be done in conjunction with a plain glass of the same thickness in such a manner that the gelatine film holding the photographic negative is Fig. 39.—Adjustable exposure frame. always sandwiched between two glasses ; then the focal length is the same for all, which enables us to give the copying camera a fixed focus for all three exposures. If one negative of the set of three is on a celluloid film, the best plan is to make contact positives. It is also advisable to use glass of the same thickness for the positives, in which case we can make the enlarged negative from the glass or film side of the positive. The different negatives and positives should always be spotted before they are used for the next process. When making glass positives or negatives from transparencies an “‘ adjustable exposure frame ” (Fig. 39) seems to be necessary. 94 COLOUR PHOTOGRAPHY COAP PE Rex _THE GREY PRINTING Pia HEN the painter has laid down the outlines of a painting \ \ he will, if using fairly transparent colours, fill in the shadows and darker half tints with grey before colouring up, and later to enhance the pure blue, green, yellow, orange and red he is sure to work over the half tints with a darker colour. The deeper the half tints the darker will he use the colour ; and he has no scruples in using grey or black to set off the colours. Such method has the effect of making the colour where pure to appear much more brilliant, but with all the addition of grey and black the painter husbands the colours; he does not mix black and grey with blue, green, yellow, orange or red where such tints should be pure; such admixture in his opinion would degrade the colours and produce only night effects. | When the three-colour half-tone process came into use, the want of a grey plate was soon felt and the photographic expert thought that when taking a fourth negative through a yellow filter he would have the necessary correction or colour balance for grey. Some more economically inclined thought the blue filter negative could be used for the two purposes, wz.: a yellow printer and a grey printer. Others thought the blue or red record negative better for the purpose of making the fourth screen negative from. This would answer if the required positive was made, so that the half tints merged into the high-lights, obtaining a sort of skeleton reproduction allowing only the most transparent part to form the screen negative. Supposing now this skeleton plate, obtained from the yellow printing negative is printed in grey or black, and the yellow print from the proper yellow printing plate is superposed ; does this combination further a good colour rendering ? The expert says it does. For my part I do not believe it; if I mix black and yellow together on a palette nobody would take the mixture as an improved yellow. Why should it, if it is done in two operations by way of printing ? A certain house took up carbon printing for the purpose of making portraits in colours and thought to evolve a process of its THE GREY PRINTING PLATE 95 own. To that end the fairly permanent yellow was discarded and substituted by a bromide print toned yellow with Farmer’s mercury iodide intensifier, to which no hypo had been added. This com- pound was not stable, any alkali in liquid or gas form bleached the same, and so did the daylight. But to bring us to the point we discuss, it was claimed that if the bromide print was not completely converted into the yellow state, the remaining and unconverted grey silver compound would form a grey key, that is the fourth plate. This is in no way the case, and the idea is the outcome of want of knowledge of the requirements. The fact is, if your plate or print is not fully developed (in this case for the yellow) a flat and smudgy result is the outcome; and also yellow with an admixture of grey is not a pure or brilliant colour. In a one-exposure camera we have always one reversed negative and as a rule it is the red printing record. In a red filter negative the parts representing yellow to deep orange are covered, allowing all blue to be printed, and in a blue filter negative, blue-violet, blue and green is fully exposed allowing all yellow and orange to pass and therefore to be printed. If now we superpose these two negatives, film to film, in exact register, practically all the pure colour values in this compound negative—the colours which the printer tries to keep pure—become opaque and only the fully transparent and also some half tints remain in such a condition as to allow a good positive to be taken therefrom; shorter or longer exposure will give all variation one can require. It seems to me that such a positive if used as a basis for the fourth plate is a much more satisfactory medium for printing the grey, as it leaves all places where pure colours should be shown quite free of any admixture. 3 The taking of direct screen or half-tone negatives for colour work, has been abandoned in some houses, and the screen nega- tives are made from glass positives, of which the colour. negatives taken direct are the origin. If these colour negatives are always taken with another glass, film side between the two glasses, and if the reproduction for glass positives is done the same way, then there is no chance of bringing in unequal focal length. Therefore there is no reason why the red negative could not be taken the reversed way, and this system of obtaining the grey printing plate adopted. To my mind this system is better than any other and requires little or no faking, called fine etching, to bring out the colours in the combination print. 96 COLOUR PHOTOGRAPHY CHAPTER] XXX LANTERN SLIDES IN COLOUR r ; “XO make colour lantern slides, three part positives in colour are required, namely, one in blue, one in yellow and one in pink. These colours are supposed to correspond to certain sections of the spectrum. I have, however, used a pink of which I was unable to find the corresponding shade in the spectrum, and curiously that pink gave me better and truer results than a red, supposed to correspond to a spectrum shade. I found that a fair variation as to shade for all three colours, least, however, as to the yellow, was permissible. I have used many different reds, from orange red to magenta, rose and bluish pink, and I obtained therewith fair representations of the object in colours. If the yellow employed has the slightest admixture of orange, the harmonious colouring is destroyed, but the blue allows all the varieties that Turnbull’s blue can assume, without ‘unduly inter- fering with a fair colour rendering. These remarks are specially applicable to the aniline dyes as for transparencies, where it is easily possible to adjust each colour section to the two others. As the blue basis of our slide we can use a blue-toned bromide of silver positive, toned as described in the following chapter. The colour is very good and closely resembles the shade pronounced by the expert as greenish blue, whilst it is permanent when having an acid reaction. The yellow part positive can be printed on a separate gelatinized celluloid film or can be printed direct into the very gelatine film which holds the blue iron print itself, and to be able to do so, the gelatine has to be sensitized with a chromate, free of alkalis. This superposition of two prints on one gelatine film as here described would have been patentable, but I refrained from filing a patent, because my experience has taught me that there is nothing to be gained thereby. The gelatine film has to be sensitized, and one way of doing this is to use a large flat brush and gently apply for about one minute a six per cent. solution of ammonium bichromate, to each 20 ccs. of which has been added a drop of sulphuric acid. LANTERN SLIDES IN COLOUR 97 Another way of sensitizing is to immerse the gelatine film for two minutes in the following solution : Ammonium bichromate 6% ROECCS. PeeesOULICs e..- .. - 50% 12 drops. Duetemmorcdinary... .. -.. ..-- 60 CCS, It is advisable in both the above cases to pass the plate thus prepared quickly through some clean water to eliminate the surplus sensitizing solution, before putting the plate up to dry. The dry chrome-sensitized blue-toned positive is put into register with the yellow printing negative record, or the plain sensitized film is printed in the orthodox way, and the printing is done in the direct sunlight. For a medium strong negative the exposure is about ten minutes. When printed the chrome positive is then ready to be washed free of soluble chrome salts before it is coloured up. For the red part print, a reversed negative, such as the one- exposure camera gives, is of great utility, as then the cover glass can be gelatine-coated, and also chrome-sensitized ; if, however, all the negative colour records are same sided, then the red should be printed on a gelatine-coated celluloid film, or the negative can be printed through the back on to the cover glass, when naturally some unsharpness will be introduced. To obtain a gelatine-coated film or plate, ordinary dry plates can be fixed out, well washed, dried and then chrome-sensitized, or it is also possible to coat plates, either with plain gelatine or with a warm and filtered chrome-solution of the following composition :— Gelatine, Coignet’s photographic .. .. 18 grms. Water,,ordinary <. .. ge See ZO ECCS: Ammonium Paul, 6% iia ie TOsccs. Polgesuonuric, 507, stock .. .. .. §20 drops. This is sufficient to coat fifty quarter-plates. The plates before coating are properly cleaned and dusted, warmed and placed on a level slab. By means of a measuring spoon the solution is poured on the centre of the plate and the flow is assisted by the same utensil. When the coating has become properly set the plates are stood up on a drying rack and slightly heated air may be used to dry the plates quickly ; not more than ten hours should be allowed for that pur- pose. If, however, the plates are overheated, the bichromate will be decomposed to a lower chromate, and when printed will show 98 COLOUR PHOTOGRAPHY bluish on white, whereas if correct the print shows a good brown or very light brown, which colour will not completely disappear, when the plate is freed of the soluble chrome salt by washing. The faint colour remaining is of no consequence, but could be eliminated with a weak solution of sulphuric acid, partly to the detriment of the positive. The colouring of the chrome prints is done with aniline dyes and they have to be fast and acid-proof; for this purpose acid yellow and acid red are used. If acid added to a dye solution de- composes the colours or changes the shade of them then they must be rejected. The strength of the colour solution is about five grammes of colour to a litre of water, and it is acidulated with twenty drops of acetic acid. If the colouring is done in neutral or alkaline solutions the same will be very irregular and in some cases no proper colouring takes place, nor can proper transparent whites be obtained afterwards, the gelatine remaining stained in all parts. This is especially notice- able with the red prints. The chromated plates are printed till the picture is well seen in a brownish colour; they are then removed from the printing frame, well washed for about half an hour in frequent changes of water. Washing in running water is not to be recommended, as it tends to very irregular washing out of the chromates and through that to irregular colouring. When washed out for sufficient time, the plates are immersed in the respective colouring solutions for twenty to thirty minutes, so that they become coloured through and through. If the plates when coloured show a slight positive, or show no picture at all, they are in the best of condition; if they attain only to a negative the time of soaking in the colour-solution should be doubled. Freshly made colouring solution is recommended ; it can, how- ever, be used twice or three times in the course of a week or two. If sufficiently coloured the plates are then washed in repeated changes of water, when the pictures will gradually become clear colour positives. Theless exposed or less hardened parts release the colour quicker than the well exposed and more insoluble parts of the gela- tine. The coloured plates can be stored before washing out any of the colour, or may be partly washed out and the complete washing out can be done at any time. This washing out of the colours may take up to one hour with the yellow and up to several hours with LANTERN SLIDES IN COLOUR 99 the reds. With the reds a few drops of ammonia can be added in the last waters; it helps to clear the high-lights; but ammonia must not be used with the yellow when blue and yellow are in one gelatine film, because ammonia in small quantities will give a violet colouring to the blue, or in slightly larger quantities will dissolve the blue, because Turnbull’s blue is soluble in all alkalis. Practically any acid added to the last washing water will keep the blue in good colour and also will fix the colours sufficiently. ' When a certain experience has been gained one is able to judge with fair correctness how far the positives have to be cleared of the superfluous colours. When the latter point is reached, to prevent markings and irregularities, the water has to be mopped off, with a soft cloth or blotting paper, and the plates have then to be dried. When dry the blue, yellow and red positives are superposed and the artistic test will tell which-colour has still further to be reduced by a renewed washing out. It is this balancing and adjusting of the colours which is a great advantage. I have tried to apply the same process, to making prints which are viewed by reflected light. Blue and yellow on an opal glass do very well, but on a paper the yellow cannot be properly washed out of the whites. Some ingredient of the paper composition acts as a mordant and takes up the colour as a fixed dye. There is also a drawback with the red stained positive when printed on a glass, and in that state superposed on the blue yellow combination, because it will always reflect predominantly the top colour. For this process I have also tried to make a stripping gelatine film on a collodion basis, but the latter also takes up the colour as a fast dye, preventing thereby clean and clear whites in the high- lights. A further disadvantage is that the two insoluble surfaces refuse to properly adhere to each other with best glue; the top picture will peel off, the surfaces being evidently too glossy. I indicated that in the last stage of washing out the red colour a little ammonia could be added to the wash water as a help to clearer high-lights, and this addition does not affect the sharpness of the colour positive ; I think it rather helps to accentuate the sharpness. This is, however, not the case when adding soda carbonate or similar alkalis ; the colours seem to spread out or run, similarly to a drop of colour on blotting paper. Dr. Jumeaux is the originator of this process. 100 COLOUR PHOTOGRAPHY CHAPTER XXXip BLUE TONING bromides are often required, but the different processes known at present for toning a bromide image blue, ive, as far as I have tried, no satisfactory and regular results. When using a direct toning process, that is, toning at one operation, we find that the image is intensified in a manner not very controllable, and is too often blue over-toned to the detriment of the finer details. If we take twelve pictures and tone them one after the other, we obtain twelve pictures differently shaded in blue. The first toned picture has a colour resembling indigo with probably clear whites, the last toned picture has a milky blue appearance and there is no white where white should be pure and clear; it looks as if the gelatine had also been toned, as well as the picture. With the process known as the indirect toning process, first bleaching and conversion into blue after, I also obtained nothing very satisfactory. It did not much matter if the solution was acid, neutral or ammoniacal. After experimenting for a long time and in different directions I thought that the red prussiate alone did not convert the bromide of silver into such a state as to be easily converted into blue, and I looked out for chemicals assisting a better bleaching. At last I found a process which gave me absolutely sure results either for glass positives or paper positives and, moreover, in such a blue as is required for the blue part print in colour photography. The bromide positive is bleached in the following solution :— Pe= colour transparencies and other processes, blue toned A. Freshly made red prussiate solution 3°% 100 ccs. Soda carbonate stock 10% ae ss TOgss Ammonium nitrate stock 10%.. a 10, Chloride of sodium 10° < = 10s If we change the soda carbonate for ammonia the conversion to a blue picture will be weaker and the tone will be more blue violet or ultramarine. BLUE TONING IOI The above bleaching solution decomposes slowly, but will act well for about half an hour, and the given quantity will be suffi- cient to bleach about twenty-four half-plates. The grey black of the bromide of silver will not be bleached out to a white, but will be converted into a picture having a light grey-brown appearance. Before immersion in the bleaching solution, the dry positive should be moistened for a few seconds in ordinary water. This will help to equalize and regulate the action of the chemicals. The bleached picture, after being well washed, is converted into a blue in the following solution. B_ Potass. bromide stock 5%, 10 ccs. Acetic acid stock 10% Loves Iron alum stock 3%, AC ame I generally use ammonium iron alum. This solution B de- composes fairly quickly, and is only sufficient for about twelve half-plates. The acetic acid can be replaced by one per cent. hydro- chloric acid, but the toning solution is thereby more quickly de- composed. When the pictures have attained a milk blue or steel blue appearance then the toning is complete; to tone longer is not injurious nor will the tone be changed. After the toned positives have been properly washed, they are again fixed out for five minutes in a five per cent. solution (preferably acid) hypo and after a good washing they are cleared in a one per cent. solution of sulphuric acid for about two minutes, which must be followed by a last short washing before the positives are placed on the drying board. When using the above toning process, the original positives have to be developed to full strength, because there is no intensifica- tion by this process; if anything they will be slightly lighter. The white parts will be absolutely clear and not over-toned in any way. The gelatine is not affected nor has it any influence on the results if the positive remains a little longer in one or the other solution. A further advantage is that toning by two operations does not tone or colour the fingers at the same time, and the vessels employed will also remain clean and clear, for the simple reason that the solu- tions form no incrusting or precipitating sediments. If the bromide of silver positive is found to be too dark, it can easily be made lighter without sacrificing the half-tones by immersing in a hypo bath to which has been added some red prussiate and a small dose of soda carbonate. The latter addition imparts a quick 102 COLOUR PHOTOGRAPHY and equal action, so it is advisable to make the reducing solution not too concentrated. Like all other bromide of silver prints converted into yellow and red, the blue toned one, if too strong, can be reduced by an alkali treatment. A week ammonia solution will attack the high- light more than the deeper coloured parts, whereas a weak carbonate of soda solution will act just the reverse way, and the prints by the latter treatment seem to lose in sharpness. If the alkali acts too long the print may entirely disappear. After the few seconds necessary to reduce the toned colour print, it is washed and fixed in a half per cent. solution of hydrochloric acid. However, prints treated in this way do not seem to be so permanent as the undoctored ones. CARBON PRINTING 103 Sri EL ERO SITE. CARBON PRINTING \HE colours which can be used as pigments in the carbon process are very limited. We have only an insoluble violet- 3 blue, not a green-blue as required; for the yellow we have only metallic oxides which are in no way transparent ; and for red only the madder red of organic derivation. It is also possible to use alizarine as an aniline lac, and as such is liable to make the gelatine irregularly soluble, like all lacs do. The reds have an orange tint, they are not pure pinks. The printer using fatty inks has a better colour range at his disposal; solubility in water does not hinder him in using such colours. The carbon pigment papers, also called carbon tissues, on the market are anything but colour correct, or even uniform in working. If prints are made from one negative only, say one print in blue, another in yellow, and a third in red, we find the developed blue print hard, the red too flat and the yellow right, if all the tissues are treated alike throughout. For our purpose, however, the blue print should be flat and very thin, because blue has the greatest covering power in combina- tion with the other pigments; for the red print more contrast is desirable, because the red has distinctly less covering power in the stronger portions than in the thinner and more delicate parts of a print. These phenomena will give the clue as to why a thinner negative is preferable for a blue record, and shows that a contrasty negative should be employed to print the red from. A strong negative is also required for yellow, because no transparent yellow exists fit for such printing, and on account of this opacity the yellow is used to form the first print near the paper. A fuller initial con- trast is a necessity to bring the yellow to effective account so as to shine through the other two more transparent colour superpositions. The yellow is therefore subject most to the influence of the ground- glass variety, as explained before in an illustrative way. Suitable for our purpose we find three-colour pigment stripping films on celluloid on the market, and also carbon tissues on paper supports, the latter are much cheaper and give much sharper 104 COLOUR PHOTOGRAPHY pictures, because the former have to be exposed through the film thickness, and the latter are exposed direct on the tissue. The manipulator who develops a carbon tissue on a collodion film, or on an india-rubber coating, supported on glass, has the advantage of being able to use water of any temperature, enabling him to clear the print perfectly of any superfluous matter; he has not to be afraid of cockling his support or losing it in the developing . solution, and if he has once used the glass support he will find it to his advantage to always adopt it. When printing with the sensitized carbon paper, we have to print the yellow tissue till the image is visible as a brown-orange impression on the yellow surface ; we can thereby very easily judge the depth of printing. The print on the yellow tissue can therefore be made use of as an exposure meter, because the other two tissues show no such change when exposed. If the yellow print takes fifteen minutes for full exposure, then the red would take about twelve minutes and the blue six to seven minutes in case all negatives are of the same density. The correct shading of the blue is the most difficult to attain and it is on that account ada to print the blue in duplicate. The blue printing is the difficult one, as I have said before, because blue possesses greater covering power and also because the blue pigment does not absorb the light actinity, like the other carbons. To counteract this as much as possible and to reduce the pene- trating action of the light, as well as to prevent the formation of a deep relief, I have tried to add soluble yellow colour, forming quasi a stronger yellow light filter than the chromate can form. By ex- periment I have found that such addition is best made by adding the water-soluble colouring matter to the sensitizing bath. This addition to the blue tissue I found of great advantage, but of no influence on the yellow or red tissues, which allow us to use a uniform sensitizing bath for all tissues. The sensitizer for carbon tissues I recommend as follows :— A. 10 grammes of potassium bichromate dissolved in 250 ccs. of water, neutralized with ammonia till the orange colour has changed to yellow. B. 10 grammes of potassium bichromate in 250 ccs. of water and when dissolved add two grammes of tartrazine or any other similar colour that is not thrown out by the chromate. A and B are mixed, and used only once when cold. CARBON PRINTING 105 Enough solution should be poured into a dish to facilitate a proper floating of the tissue. Immerse the same for two minutes, giving the proper attention to turning it over and of moving the solution to facilitate an equal sensitizing; then remove from the solution, pass the tissue through clean water for a second or two, place it face down on a clean slab or glass. Remove with a squeegee all fluid, and then wash or rather mop the back of the tissue with a sponge to remove superfluous sensitizer and all running liquid so as to facilitate drying, finally hanging up the tissue to dry ready to be used next day. I do not recommend storing it in calcium tubes, because a small amount of moisture in the tissue is necessary ; absolutely dry tissue is too brittle and does not print properly. It is naturally possible to use older tissues, but if regular work is valued and desired, and as it depends on equal sensitiveness of the tissue, then put up with one rule and stick to it. In warm weather, when sensitizing, put your dish holding the sensitizing solution into a larger dish and allow the tap water to pass into the larger dish, thus keeping your temperature below 16° C, (60° Fahr.) In calculating the exposure necessary for carbon tissues, I find a Bee-meter also very useful; the time of darkening the dark tint multiplied by fifteen during mid-day is near the mark, as required for the yellow tissue. é 106 COLOUR PHOTOGRAPHY CHAPTER Xo. xe CARBON TRANSFER one red), we have to develop them and for this purpose I re- commend the collodion transfer process. Select the glass to support your prints of such quality that it,is free from specks and let it be larger than the print to be mounted on it. Wash the glasses well and polish the best side up. Charge a cotton tuft with dry French chalk (“ talc ’?) and apply it with gentle friction to the clean surface, dust, border the plate about a quarter- inch wide with a thin solution of india-rubber, to destroy the slippery surface and give to the collodion an edge for firmly attaching itself to. On the surface not prepared, stick a small paper mark to pre- vent any mistakes. The india-rubber solution is prepared by dissolving a little pure rubber (not vulcanized rubber) in chloroform, and the perfectly liquid solution is applied with a small soft brush by passing once round the border of the plate. Collodionize the prepared plate surface with a three per cent. enamel collodion, and when the collodion has set, immerse in water till all greasiness has disappeared before surfacing with the carbon tissue. I recommend large tanks with grooves, so that a number of plates, say one day’s requirement, can be prepared and kept in the water. All collodionized surfaces should be turned to the left side, the side of the thumb, and the tank should be marked accordingly. Preparing the plates in such a way in advance has no deleterious effect on them, and we have in this way the vaporized solvents only once in the house during the day. I once prepared collodion plates, stored them dry, and soaked them in water before use, but I found that the collodion film gets too horny, and the gelatine film does not enter into homogeneous contact, which is shown by the air bubbles formed between the two films, and these are multiplied by the following application of a squeegee. | |: we have printed the four carbon tissues (two blues, one yellow, CARBON TRANSFER 107 Have your collodionized plates ready to hand, then prepare a dish with cold water, not over 18°C. (64° Fahr.). Immerse one carbon print in it, turning it over to eliminate all air-bells from the surface of the tissue, take note of the time it requires to get flat, which will be about sixty to ninety seconds, then, without losing a second, lay the tissue, film down, on a wet collodionized plate, cover with a protecting cloth and pass your large squeegee with one firm stroke over the lot, which should give proper adherence to, and eliminate all superfluous water and possible air-bells from between the two films. Then with the aid of blotting paper mop up all - moisture from the back of the tissue and let it stand for ten minutes. In the meantime, the same operation has to be performed with the other tissues. Be sure that the time of immersion is exactly the same, because that is the condition for securing equally expanded films. After having allowed ten minutes for each mounted tissue to dry, ensuring proper adhesion, soak it again in cold water, not less than five minutes, but not more than two hours before developing in warm water, see also that no air-bells are formed outside when putting it in the cold water again. Before starting to develop, have a fair amount of warm water ready, so that you can afford two or three changes of water for the express purpose of ridding your carbon film of all chemicals and soluble colouring materials. When ready to develop, immerse your glass holding the print in water of about 40 to 45°C. (104 to 113° Fahr.), and when the known characteristics show that the paper can be removed, do so with a steady pull without rubbing the tender film on the collodion and take equal care in clearing the print. Warmer water can be used if necessary, but do not use force or work with undue haste to clear the prints; the penalty is irregular and hard prints. Remember that these colour tissues do not dissolve so quickly as ordinary gelatine. The appearance of the print should be delicate and of about half the strength required for an ordinary one-colour print; if too strong then an addition of a few drops of ammonia to the developing water may remedy the defect a little. When sufficiently developed rinse in cold water and stand up to dry. Instead of collodionized plates, india-rubber coated plates can be employed, the rubber solution being of the consistency of treacle. When the solvents have evaporated, the plate is ready to hold the tissue. 108 COLOUR PHOTOGRAPHY The text books say that sensitized carbon tissue in a wet state is no longer influenced by daylight. This is a fallacy; what is true, however, is that the sensibility to light has been reduced to half or one-third. The deleterious effect of exposure to daylight even during development is very quickly noticeable, when the three prints are superposed, therefore keep the wet carbon print, as long as it contains the slightest trace of chromate and as long as the same is not fully developed, guarded from daylight or actinic light. The three part prints have to be dry before they are ready for superposition, and for that purpose we require a solution of glue. Best light-coloured transparent glue about 20 grammes is dissolved in 500 ccs. water. If the solution when cold keeps liquid, then our mounting solution would not act properly. I say this because by introducing wet part-prints and wet collodionized plates we con- stantly add diluting material to the glue and if we desire to use the glue solution from day to day, we must keep it up to the required strength. The other extreme is a glue of stronger percentage than is required, because it would set too quickly and thereby prevent an easy superposition of the prints. The paper on which the three part-prints are superposed should be of good quality and hand-made paper is very good. Sawyer’s Temporary Support (No. 112) if used on the side not prepared is acceptable. I have made experiments in the direction of non- stretching paper and I think the following is perfection. Take the best quality glazed baryta paper and collodionize each side, use when dry. The paper prepared in such a manner does not stretch and has an unchanging white of the most approved quality. When ready with the preparations, warm the glue to about 50°C. (122° Fahr.) filter through fine muslin into a dish, which should be kept warm by some means. Immerse the glass print in the warm glue solution for two minutes, so that the glue is properly soaked into the print and the glass itself becomes warm. The water-soaked paper is then also passed through the glue solution, paper and glass print are superposed, the squeegee is applied, but only so that all superfluous matter and all air-bells are eliminated. There must be enough glue left to fill up the paper pores or any amount of air- bells will appear when the transfer is complete, showing thereby that only part adhesion between the two exists. It is the yellow print that has first to be mounted, and when the operation has been performed, mop up, with the aid of a sponge dipped in warm water, CARBON TRANSFER 109 all superfluous matter, then stand up to dry in an even and not forced temperature for about twenty-four hours. When this yellow transfer is dry, cut through the collodion film at the border of the paper and lift the print off the glass. If the print does not detach easily and properly, it would be an indication that the print is not thoroughly dry or that the talc has not filled up the glass- pores. The other two part-prints are mounted in a similar way, leaving the most transparent for the surface print. In mounting the second print, immerse the print again in warm glue solution, and also the yellow print, which latter should have been soaked in a five per cent. formalin bath for ten minures and well washed before putting it in the glue solution. The two are taken out together, squeegeed, and with a warm sponge and warm water the plate is cleared; it should also be kept warm so that the final adjustment of the two prints can be done before the glue sets. When the two prints are in perfect registration allow the glue time to set firm, before the prints are finally cleared of the superfluous glue. When dry and detached from the glass support the third print is mounted in a similar way. A preliminary superposition of the three part-pictures when still on glass can be made, and to prevent damaging the delicate picture film, paper wedges between and at the corner of the glass must be inserted, but no accurate judgment or anything near it can be gained. The internal reflections, in the glass and also the dimness of the pigment film gives it the appearance of irregularly coloured ground glass, thereby preventing correct judgment even when superposed on white paper. When the composite print after the third superposition is dry, and detached from the glass, keep under pressure for a time, so that it is made to lie flat. The picture will be glossy when taken off the glass in a dry state. For an experienced man it would be possible to take the last print off the glass directly after the glue has set, when the print will be matt. The retouching and spotting of this three-colour print is not very easy, but if prepared oxgall is used with prussian blue, cadmium yellow, and alizarine water colours, small defects may be remedied. It should be remembered that an orange-red spot is to be subdued with the complementary or missing colour blue, yellow with blue- pink, blue with orange, and green with pink. 110 COLOUR PHOTOGRAPHY CHAPTER XXog\s CINEMATOGRAPHY IN COLOURS producing the first result in Cinema work with two colours, have asked me for an article on this subject to be included in this book. The two methods of colour photography have also impressed themselves as a natural consequence of the existing knowledge in colour photography, in the moving illustrations of daily life. Mills, I think, is the only one who had some success with the subtractive method of colour photography. His results, which were fairly good, were shown in private about 1914-15; the subjects shown were very slow-moving or nearly stationary subjects. The printing of three different colour films in superposition was a long affair, and very likely the commercialization fell through on that account. Up to the present the semi-additive methods have shown no results, because, when enlarged on the screen, the grain or the separate particles of the three-colour basis became too discernible to the eye. They can no longer amalgamate in a harmonious and homogeneous unity ; also it is not possible to multiply the one film for the service of the million. The main and principal direction in which cinema in colours can be made of use is, to my mind, by the addition method pure and simple. Colour cinematography by the addition method was inaugurated by Lee and Turner, Pat. 6202/1899, at their St. Ann’s Well Studio, Brighton, but no results seem to have been obtained, mainly through want of a good colour sensitizer. Azalin was not rapid enough. Orthochrom T. was discovered about 1902, and Pinachrom a year or two later. The first result in cinematography with two colours was obtained by Davidson and Jumeaux on a small glass plate cinema camera in 1902, but the patent embodying the invention No. 3729/1903 (see Fig. 8, Exterior Prism position, Page 18), was worked on an Mi: publishers hearing that I am a worker who assisted in ‘uaa13-an[q ul pr9afoid aq OL CINEMATOGRAPHY IN COLOURS III ordinary cinematograph camera; two pictures side by side (see Fig. 40). The light filters were stationary, therefore the exposure was simultaneous. The exterior prism position first suggested by Dr. Jumeaux was the formation used by N. W. Lascelles Davidson in producing his cinematographic pictures in two colours. The results were first shown to the Photo- graphic Society in Paris, 1st May, 1904, and later at the Brighton Hippodrome, Nov., 1904. This process of obtaining two pictures by the aid of two prisms and one lens, was later followed by Albert Smith’s process, 26671/- 1906, exposing one picture after another, also alternating the light filters for each exposure. The different light filters were placed on the moving shutter. Both systems gave colour pictures tainted by colour fringes. The defect in the first process is explained in Chapter VII., as derived from the prisms. The defect in the second is really obvious, irregularity caused by two exposures, which the persistence of vision was not able to assimilate. It is of absolute necessity that the colour selection and therefore the exposures for two or three part colour record negatives or positives, must be simultaneous. Instead of using light filters on the camera shutter some inventors have thought to cir- cumvent Smith’s patent by joining up the filters on an endless or circular band and pass them during the exposure in front of the Fig. 40. sensitive film, and it was also proposed to colour the positive film to save using the light filters; the colour fringes were not removed, seeing that the exposures were not simultaneous. It has now been proved that a slight stereoscopic difference, where the lenses are placed vertically instead of horizontally, does not show as a whole the colour fringes to a noticeable extent. Nearly everything in Nature moves in a horizontal direction—the man, the To be projected in Orange. II2 COLOUR PHOTOGRAPHY vehicle, the train, the wind, etc.—and the movement in a vertical direction is really very small. The first indication for such a purpose and the possibilities of such a battery of lenses is given in the English patent 25908/1906. The peripheries of the lenses where they join are cut away to bring the lenses more together, making effective use of the optical centres, and to shorten the picture distances; also to reduce the stereoscopic differences to a minimum. The English optical trade would not countenance such an absurd notion, but it was taken up by Gaumont, Paris, after the English patent had elapsed, and the invention was embodied in some mechanical means as shown in patent 3220/1912. Some unsur- passable results were shown in that year at the London Coliseum. It is obvious that special machines, cameras, projector, etc., had to be made for such work and what is more it will never be possible to do without such means. A specific work requires a specific treatment, with specific machinery, and yet to-day the wiseacres of the English cinema trade ask for new ideas in two or three colour projection on the basis of the old existing machinery as used for mono-colours. These cinema colour processes here mentioned are the only ones that have been used, at any rate I am not cognisant of others. It is true there are old and new patents galore on the subject, and they are still forthcoming. My description on the optical means in which reflection and refraction are spoken of state some critical points, and most likely may point to the inherent troubles of the new systems proposed. I find the cinema trade full of optical conundrums. KINO-STEREOSCOPY II3 CHAPTER XXXVI. KINO-STEREOSCOPY. INCE the earliest days of the kinematograph industry, innumer- Se: attempts have been made to produce stereoscopic motion pictures, yet no really practical method has been suggested so far. One might be getting pretty near the solution of this state of affairs in saying, that the fundamental laws governing stereoscopy have not been fully understood, and that it has been forgotten that the two eyes have to see two slightly different pictures. Fig. 41.—Stereo-Conundrum. Let us turn to Fig. 41, where “‘ O1 ” and “ O2” are two lights or optical centres. It will be seen that two light-cones are projected towards a ball ‘‘ P,”’ and also that the light and shadow of the combination is thrown on the focussing plane ‘“‘ F.”’ As stereoscopic pictures the two images should be a—b and c—d, but we see only c—b, for the rest has melted away. If now a positive is printed from the negative so obtained, and is viewed with two eyes, shall we see a_ stereoscopic representation of that ball? Of course not. Yet many an inventor has said he does, and has based patent after patent on that impossi- bility. So far as the negative is concerned, where two shadows meet we have transparency, and where one light-cone passes over the shadow of the other, no transparency will be obtained; nothing II4 COLOUR PHOTOGRAPHY but one deformed composite picture, flat and without any stereoscopic properties. Such a picture is worse than would be obtained with one lens only. t , Ox \" O2 | : S. 2 “'G ie : MS EE Bek RS Mi Fig. 42.—-Kino-Stereoscopic Taking Device. For the purpose of taking stereoscopic pictures a ‘‘ Kino- Stereoscopic Taking Device”? (Fig. 42) has to be employed. In this two lenses placed at the eyes’ distance apart—that is, 3 to 34 in.— form two light-cones at the focussing plane F1 and F2, when two separate pictures are impinged on the photographic film. Each light-cone is twice reflected, at “M1” and “‘ M2,” to form a narrowed down picture in the small focal plane. The reflector “‘ Mr” is best formed by a right-angle prism, a—b—d ; ““M2” can be part of a right- angle prism “‘P,” preferably made of black glass, or a right-angle prism c—e—g with a silvered surface. ‘“‘ M2” can be a part of a—c— e—d a form of solid reflecting prism, or an air prism. Additional enlarging or reducing lenses (S or L) can be inserted anywhere in Fig. 43.—Sight Transposing Prism. the light-cone. With such a device we obtain two negative pictures side by side, somewhat dissimilar, but of the identical view in general. The size, however, is somewhat restricted. After having obtained the negatives, as explained above, posi- tives have to be printed therefrom, and when placed in a contrivance suitable for viewing them, the combined pictures will show in relief, that is stereoscopically. For such a purpose a “‘ Sight-Transposing- KINO-STEREOSCOPY | IIs Prism” (Fig. 43) comes into play. Such a prism obviates the separa- ting of the film and transposing the same in printing. The light-ray **C” enters the first refracting surface “‘ Rr,” and is deviated from the straight course to the second surface “ R2,’’ where the same ray is reflected to ‘““R3,”’ and is there a second time refracted at the offside of **R3.” The prism has at ““B” an angle of about 76 deg., and to prevent the possible overlapping of the picture a partition ““H”’ can be cut into the prism. If now we place such a prism into a “‘ kino-stereoscopic viewing device ” (Fig. 44) we can see the positives stereoscopically ; Fig. 44.—Kino-Stereoscopic Viewing Device. The light-cone on the left side, coming from the excentrically placed ocular “ OI,” is passed over the mirror “‘ M ”’ (forming part of a right- angle reflecting prism P), showing us the picture placed at the right side in “‘F2.” Supplementary lenses may be inserted anywhere in the single light-cones. The pictures are seen across each other’s light- path. Therefore, the eyes will see the two different pictures in the correct position, 7.e., in the right position to be amalgamated by the human sight nerves into one picture in relief. The positives obtained as above can also be projected on the screen ; in that case, one series, say the left, is projected through a green colour-filter, and the right through an orange-red one. The two pictures are projected together in preference, superposed or part superposed, which is effected with wedge prisms or wedge lenses placed in front, or at the back, of the projecting lens in a projector of the ordinary type, which has been altered to take films of double width. The stereoscopic effect is obtained when viewing with similarly coloured spectacles. I may say here that, in my opinion, those who think they will see stereoscopic pictures on the screen without such selective colour-filters will always be disappointed. The arrangement in Fig. 42 lends itself admirably to a modifica- tion. The light-cones have not necessarily to be formed on a level, 116 COLOUR PHOTOGRAPHY. but can be placed one above the other as shown in “ kino-stereoscopic taking and viewing device’ (Fig. 45). Personally I have made no experiments on this line, but simply suggest that the working is correct. In that case the left side prism, with its base “O,”’ and the right side prism, with its base “‘ P,” form the two picture planes “ F1 ” and **F2,”’ one above the other, so that films of ordinary width can be used. When viewing the subjects in the instrument, the positive obtained on focussing plane “F1,” has to be shown through focussing plane ‘‘F2 ”’ in the other light-cone, and vice versa. Projection on to the screen can also be accomplished by the same instrument, or by a projector having a movement of two pictures. In the latter case the two WW CX WO WH. ame 5 a WHI mass NY Fig. 45.—Kino-Stereoscopic Taking and Viewing Device. pictures would be projected together with one lens, and a better super-position would be obtained with wedges, as explained before. Another method would be to use an ordinary projector with a standard movement, which should bring the red and green images, by per- sistence of vision, to the eyes, as stereoscopic pictures. In all cases selection by colour-filters comes into play; were they omitted a frightful flicker would be the only result. There is also the possibility of taking two pictures spaced on a film running horizontally, direct and without any reflecting device ; the superposition of the positives by the aid of wedges and colour filters can be done through the same instrument. The taking of two pictures at the eyes’ distance on two vertically running films has been tried already, but it proved a failure, because the corre- sponding pictures were so easily lost, nor did the inventors use selecting colour-filters. The above, I think, clearly sets out the basic principles of the subject of stereoscopic kinematography, and as a result many would-be patentees should be saved much misdirected trouble and labour. INDEX Abney, Patent of Absorption of Filters Absorption of Secondary Rays .. Absorption of Transmitted pea Acetic Acid, Use. of.. = : Acetone Acid Yellow Additive Light Projection .. Additive Method a Additive Primary Colours . Additive versus Subtractive Alcohol, Solubility of Dyes in Alkaline Bath : Alum Substratum, Effect of Amidol Developer § Ammonia for Washing Out Colours Ammonia in Sensitizing Solutions .. Ammoniated Fumigation Ammonium Nitrate Ammonium Picrate. : = Anomalism in Reflector Cameras | Arc Light Atmospheric Influences Autochrome ... Fan Azalin Balancing of Light Filters and Plates Barnard, Patent of. : Bathing Dry Plates Bennetto, Patent of Bichromate Sensitizing Bleaching Prints Blue Dyes Blue Filter Blue Printer Blue Toning Bromide Plates Brown, Theodore, Patent of Bromide Prints Butler, Patents of piled S7ase0s0m 7 5254073 61e-81)- 08. 101 61, 70, 75 80 -.99, 102 65, 67, 68, 72, 104 (12, 13,14, 48.39, 40,43, 46, 54 97, 104 sis 100 eA Si 69, Te iol O : 10.103 100 67 aR 11 38, ep 95, 96, 99 9,13 Cameras 2, 3, ge5..0,9,010,°12, 1316,18;520). 24, 26, 27,30, 34,38, 39.40, Calcium Tubes Camera Extension 42, 46, 47, 48, 76, 83, 84, 86 Sie 105 44 X1ii. INDEX. Camera Construction Canada Balsam Carbon Pigments Carbon Printing Carbon Transfer Celluloid Films ws Cementing Colour Filters ... Change of Light in ea: Chloroform : Chloride of Sodium . Chromoscope Chromogram ... Chromo- “Lithographic Colour Prints Cinematography in Colours Circular Distortion ... : Cleaning Negatives ... Cleaning Reflectors ... Collodion Films Collodion Plates Collodion Transfers ... Collotype Process Colour, Correct Reproduction Colour Fringes ioe Colour Enigmas : Colour Kinematography Colour Prints a Colour Records Colour Screens Colour Sensitizers Coloured Glasses Colouring of Chrome Prints Compensation Plate Compensators Compensations Compensation with Right Angle Prisms" Compensated Bennetto Camera Comparatives in Reflector Cameras Constructive Guide in Camera Making ... Constructive Block ... Copying Crags Ns FL Patent of vt Cross Form of Reflectors .. Curved Surfaces Cyanol Cyanin Cyan Print Dark Slides ene Dark Room Illumination ev Davidson, Patent of Degradation of Colours Dense Negatives Diaphragms XIV. PAGE .. 83, 86 36;°37,/62 O86 46, 50, 88, 94, 103 ie 106 ...92, 103 =F 62 77 106 aes oe A 100 4.58) TOC aie 16, 472-52 ‘s a 8 51 110 34 81 es 56 “104, 106 aoe 106 106 92 69 10, ‘24, 111 x 49 s 12 10, 49, 52 ak 69.76, 73 57, 60, TO 27s 6, 506,58, 6S. G52078 3, 5, $26, 27-2p4e ce 4 98 40, 84, 85 9, 6 34, 37, 38, 40, 47, 48, 54, 84 36, 37, 39, 40, 84, 86, 87 vas ae 36 40 42 83 86 des ie 93 4, 5, 10, 46,753 aie 10 3a 34 58, 65, 66, 68, 71, 123 cn 58,65, 67 INDEX. PAGE Diapositives ... ae ee wl oe a 92 Developing Three- colour Negatives et es ae ase sd 80 Direct Vision Camera on ets ae oe ths mi Safe 6 Dispersing Prisms ... ee ask ad Me hea a ri 1 Displacement of Focus oe oe mL ae ce he Le 41 Distorting Reflected Picture ae sie re ie Pa G5) 66, 69, 70, -71, “72, 16 fiviee cH Etching Half-tones a e hs co oP ae 91 Meacentic Lens Centres... bie “S ote ries aoe oa 12 Excentric Projection ate ae See oe a a A. ZA Excentric Stops pe re Bee i dc Het el nila o4 Exterior Focus Plane re ae Bie e oa vee 25 Exterior Prism Position .... ee ae ee + : “18, 110 Exposure Se ; = Delt oe “55, 58, O07 G...1 04° Exposure Ratio of Filters . bs se ea fee eb Une at Exposure Frame, adjustable ae ee ae i ae i 93 Films, Stripping fe ser 103 Filters, Light—3, 7, 9, 10, 13, 16, 25, 21, ea: 39, Al, 43, 53, 54, 55, 100.00; TS See Filter Colours Ha a aha eo an he Rebels rei he yes Filter Arrangement... sea ae ok cas ane are ee 54 Film Negatives ae ches ae ee ee te Ca ee aye Filter Yellow os shite aS me ‘Se ie Pea a 63 Filter Red... ae ae » ie fo: ie ‘ee shee Tu Fixing Negatives ... she ae =e ae fas ie se 81 Fixed Focus Camera : a a oe ae ae Ear LO eur Flaps for Multiple Exposures oe Hee ene ak i ae 43 Flowers, Photographing .... RSL Pi, Be oe ae oe ae 78 Fluoresceinate site 59 Focus ae GO; 14, 18, 20, 25; 26, 27, 29, 34, an 40, 48, 54, 85, 87, 95, HOCUES.NE Pianes—6, peetieel el 4a), L021 24.25.2206, Ai 20 aU G4 OO. aly 39, 40, 47, 48, 54, 55, 63,076,-83,-85.-86:687,. 88. 116 Dees a ee san 70 Gelatine, Coating Films and Plates with ie 5. me Se 97 xXV INDEX. PAGE Gelatine, Coating Filters with ... sae = - Sa a 60 Ghost Pictures usd pis ae ne Fe og 18; 19.26 GreenaDyess 0 ee Zot ine ok 61, 70 Green Filters a ee ee 55, 58, 61, 70, 71, “72, 73, COmto) Grey Printing Plate, “The are Sue fos 94 Glass, Cleaning ea ae ie ae dss EB ¢ a ae 106 Glass, Coloured fee Se is ee ‘ades a Pas 5. 495 57 Glass, Ground Be eS Age ie ete =e we 49, 50 Glass, Optical vas Heo ds ue ee ee 14, 26 Glass, Parallel 55 re = ih hse om aoe 14, 21, oo (oan Glass, Plate ext i ve tah tg ae 60 Glass, Platinized He 4 ae Es a at: aie 27, 43, 56 Glass Reflector <3 uae ne, Be Sis st oa 14%) 27,29 Glass, Silvered ao ea aca a ay ae « 2p Aiea Glass, Varnished ae na ee re or ee + 212 DO Half-Tone Screen ... aa ah ee noe ier 44, 91 Hamburger & Coston Patent oy: set ee fe met. fn 34 Hydrochloric CIC ae ‘ 23 n' as se me 101, 102 Hydroquinone in Developer id ae Mer af fas ie 80 Hypo My ae cas - os aa Te 81, 95, 101 Illumination of Negatives ... 1 ae oe Pe ae ae 91 Indirect. Tonine Process <2 ast =e a <6 i ae 100 India-rubber Coating ee ses ae ae: en = 104, 106 Inner Focus Plane ... See ie a oe ae ee oe 25 Interior Prism Position oe a See aoe ae: a8 19 Internal Reflections Se iy ae : 2 Ct) Die. aan Intensifying ... ae sae nee ie es! ae os 81, 95 Iron Alum... * aie Sy. sa ae ait se tick 101 Isochromatic Filter . ae bk: oh ies oe ak poe Tile Isochromatic Plate ... Be me 69 Trestle es ae ae fad 5, 6, 8, 27, 33) 36, 37, “46, 47, 53, 86 Jumeaux Process oe: os on rr Fes ads ey 99,7. Tie Keeping of Sensitized Plates site a mae 2 ae ; 68 Kinematography, Colour ... be — cee ves ike 12, 110 Kino-stereoscopy ... ‘an “ee sian oe ve: 2% ; 113 Laboratory ... os ar ee ee Ese ee a. Ss 80 Lantern Slides ie ee re ae Pea wg : ae 64 Lantern Slides in Colour ... Mit ae = we a ‘ne 96 Last for Camera Construction ... nee ee as Ef: ae 86 Lee & Turner Patent ae i. Hos ss oe a a. 110 Lenses 2, 5, 6, 10, 11, 12, 13,18, 19, 21; 23) 29) 3454236 eee Light Action in One-exposure Camera ... ier ee sie ve 46 Light Action in Chromoscope ; A7 Light Cone 7g; S2105 414207. 1G: 21, 23, 25, 29, 30, Os 37, 39, “AO, 43, “44, 83, be RS a Oe Light Filters, Making of ... a a iss den san 60 Light Filters for Cinematography _ eA 1d Igeht Pilters, 327, Odeo Oe2oee7. a3: 39, 41, 43, 53, 54, 55, 57, 58, 60, 73, Tose eo XVI. oh INDEX. Light Path Light Ray 2, 5, 6, 8, 18, 19, 20, 21, 22, 25, 26, 29, 46, 47, 52, 53, 54, 73, 83, 86 Lumly, Patent of Lucas’ Process Magenta Magnesium Flash Illumination Maxwell : Methylene Blue Metol-Hydroquinone Developer Meyer, Patent of Mills Cinematograph Process Minus Colours Mirrors Naphthol Green : Negative Colour Records Genta bens’... Ocular Mirror pe 5.6.0 610,111% PAGE 9, 10 i 92 OO; 0 38 8 53 To 80 10 ae 110 A 2: 52, Oye moo, aku pA lee 2Z, 26, 43, 45, 46, 48, 91 Olsen eicaaed 16, D0; 55, 69, 70, 713, 76, 87, 94, 97 Lead ied MU de a i fen) One-Exposure Camera, 2, 4, 12, 18, 25, 26, 28, 29, or 38, 39, 43, “46, 54, 56, 58, One-Reflector Camera Optical Axis Optical Centre Optical Glass... Open Arc Light Orange Filters Orthochrome ... Panchromatic Plate Panorama-like Ganiiiiation Panoramic Effect Pack, Plate Parallax ag Parallel Plate Refraction Parallel Plate Reflection Parallel Plates ie Parallel Surfaces, Gusved ae Peripheric Projection Persistence of Vision Pfenninger, Patent of Photo-Chromoscope ... Picture Plane ; Picture Planes Pigmentary Colours... ’ Pinachrome : Pinaverdol Plate Speeds .. Plates, Colour Sénsitive Plates for One- Exposure Cameras Platinized Glass Polarized Light Effects GS Liou soe. Ven ed 13, 39, 40, 43, 46, 54, 58, 75, 83, 84, 86 2b 24 “1h, 22, 23, 29 : Me 26 fan 58 Tie Os mice : 110 O2p203,000,-00, O08eI U2 10,5 Lom Sumo a 22 vi, 20; 22 13, 41, 55 12 ’ Hiss 27, 25, 00,00 41, 48, 60 33 23 ms 116 ie 38, 40 8 85 : 4] : 2 ‘4, 49, DO a202 58, 63, 66, TORT Te ell O 63, 66, 70;-72 die : Da oa 53, D0; 58, 65, PO wCnie INDEX. PAGE Pollock. Patenteo. . ay: Ae Pe cae Pes Ane aA 10 Polychromide Printing Process: -...; 38 Positives gee bien avi 41.47, 53, 73, 87, 88, ‘90, 92, 95, 96, 99, ‘101, Bs Positive Colour Records 45 id Opie Potassium Bromide . : a so) ae ed << on 101 Potassium Carbonate? Use of ee —e os Bee ree a0 65 Pressure Devices ... ey, ix = aes ie — PPS sit. | Predominant Hue ... 44h eM =e ates ae Sy we 49 Primary Colours ae ae eee ca tee ee i Fees Printing Colours re ae a st ot he: 1, 49, 53, dBi cane Printing in Colour ... ae APs: ao aes = ie 49 Printers’ Colours ee shes a fe Be. ee cea ma ff) Prisms ae .. 5,6, 10, 18, 19,°20; 21 2ak eee 37, Ae 114 Prism Base Down Refraction a tt <2 46 Refraction Distortion bee ; ae ae 34 Refraction—5, 9, 13, 14, 17, 20, 25, 20, 27, 20088 32, 33" 34, 36, 37, 38, 40, 48, 85, 86 Refraction Compensator ... Fe oe mi bee ~ dnd; AX Refraction Defect ... : ie te fe, 16, 29, 33, 37, 44 Refraction Through Parallel Plate er Sue Aes 14 Refraction Filter... : oe sae hee ae “ek 26%" Retouching Positives =: a. ae: oe oe a bis 90 Retouching Prints ... ze res ae a ee oe Weegee i S Reversed Negatives oe ee oe - 87,. 88, 91, 93. S57 97 Reversing Prism ... sie Aon Lee ‘ak Ret ust ws 91 Safelights Pe i sph ie sa Be v8 sae Jd 81 XVIli. a Set ee ——. ee ee INDEX. PAGE Scarlet Dyes + one ie 2, af sa sai Sa 61 Scarlet Filter is os ae OY, seh oe ee ae 76 Screens ee Aa ai ane oe me bap oe 644,807 Screen, Distance ti Lap aa ae fa site ae an 44 Screen, Opening a 4 * i = 13 5 ve 44 soreen, Negatives... oe aes ae out he Ba 88, 90, 94 Secondary Light Action ... are ite ee 14 ee oe za Secondary Picture ... an Ae aot ire sa con eOr ane Ta00 Secondary Reflections me tan ee es Be ae ae 26 Secondary Focussing Plane Coen a. i ue ee ay 27 Separation Camera ... ay As aay ie ae 13 Self-Compensating Reflection Filter ES 100; we Re 3 13 Self-Compensating Reflector ms = aed pea " 38 Sensitizing Dyes an tim a, ey cra Pe 58, 63 Sensitizing with Bi- chromate he oe te tee ior 97, 104 Sensitizing Carbon. Tissue ... oe ie Ye tn bee sisis 104 Shepherd, Patent of ; oe eee nn ord oh ee 7 Shrinkage of Celluloid Films oy “ee oe nl te at 92 Signal Green . : 57 a a ae = sfc ba Silvered Glass _ fe es ie a sa oak sae be 27 Single Compensation oe. us Se ake oe es oe 48 Sight Filters ... es tee ee 5 ae ote Be 59 Sight Transposing Prism ... at oa sh ae A ae 114 Size of Images ia ve ne Sn Se a ne - 88 Sky Screening re oe i uae aoe! ,142, 44 Smith, Albert, Process of . Fi at a ee | Soda Carbonate, for Washing- -out ‘Colours ie eae O00 ta 102 Soda Carbonate in Bleaching Solution ... soy ae vn oe 100 Spectral Dispersions ant ie — ee ate Te ANS 26 Spectroscope, Artificial ay ie oT a sie : Te Spectrum, Colours. ... Ae me Ah ae te 50, 52, 53, 75, 96 Stereoscopic Camera Ee Fy a Sa ae Pd lS Stereoscopic Difference ¥e 4) x a ae 2 20, 23, 24, 111 eereoscopic Effect... an tee ad sat lO dt, 204115 Stereoscopic Reflecting Systems fe ion ve a ee S58 11 Stereoscopic Viewing Device 7B ae hs ae cas Kee 36 Stereoscopy, Kino. ... oe “is Hee r je ay gn 110 Stop, .hree-spaced ... te es ie oe oe es wes 12 SSLODS >. '= a er oe ap es my ms is 44 Stripping Films ee ay 99, 103 Subtractive Method eel; 4, 4, 8, “ies 16, 20, 24, 39, 46, DUD Ao Ler Subtractive Colour Camera Ss Se 13 Subtractive Light Projection oes wee ny. o. =e gs 46 Subtractive Primaries op ae ed ra . TE on 52 Sulphuric Acid ay a ye ree ie oe as O77 101 Supplementary Lenses ve a. be ree a ee ae we Tare zine § —... eg ee za ee hae 61, 104 Temperature of Laboratory i ait re she ee es 80 Tension by a Gelatine Surface ... fi ee a oe mae 35 Testing for Size of Images ca ain nce or a xe 87 Theoretical Light Filters ... re pes i ao Py are 57 Theoretical Primaries ee iis ate oe ate th fied 52 1 INDEX. Three-Colour Blocks a nae oe e. ee ie eas 46 Three-Colour Prints es ae oy ons we eae 2.40 ok Three-focus Instrument ... oh er = fae oa; aoe 48 Toned Bromide Prints ce ave oe ae eo 88, 95, 96, 99 Transmitting Reflector th sie ke ae ae is 26, 43, 55 Transmitted Light ... Arf: ase Rs Res aes is Pe be Transmitted Pictures ae ans Poe ats iG ‘ 21a Transparencies eae ae Ra sie & ee 49, 73. 93, 96 Transparent Colours ee “ey es Le 94 Transparent Reflectors be ee? ae ean 2, Gy 6, 8, 10, 26, 30 Trio of Lenses ae a ie + des i Oe V2 Triple Camera ae M & ace Bx: Bone a 7, 8, 11, “02; Al has Turnbull’s Blue 40 nae ae ee ee 5 eed ... 96, 99 Two-picture Focus.... - ae oe ue ee oe woe h BIEZS Two-reflector Cameras a att so e? on me ... 47, 86 Unsharpness of Image Sey ae a Sak a a oe 29 Uranin Siok ane re af sa ea ie ono) DOR OF ies Uranoty per. an or a es ae ne ve Fae 88 Varnishing Colour Filters ... AS ae fe Lee sau ae 60 Verdol ; oe + ne ee. jst ee a3 65 Vertical Refraction A ae ae od a a ne ee oa 14 Viewing Instruments ee ee ane 4, 8, 47, 48 Viewing of Colours by Reflected ‘Light A ae oe afc pe. 99 Violet Crystals ee wae see os ae “2 Leen Violet Filter ... Se ole iiss ae ae Te ott ae 75 Washing-out of Colours... Ss ae ie mie ee: el 98 Wedge Prism Compensator ea ia sa es SY Wedge Prisms sig me se wes ~eg ipa 18, 20, 27, 37, 115 Whites Patentyot.i..: ee ae ce " we : 7 VOVORN CEG 9 es nat ar aise ee ue ~~ ee ae 70 Yellow Dyes... ee ree a ae owe Fes ce Olseg0 Yellow Filter... Aw uae ie ate ae. mat O23 76 Yellow Print a w2 cae coi oe oe 69, 94, “103, 109 Yellow Record : fz: Ge es ae a 69. 72,383 Yellow Reflector Filter we Ley ae aa ae ee ae 32 XX. aie re", rm AM oaks a > hea See a ate a eas rer eat