A MANUAL OF PHOTOGRAPHIY. A MANU AL OF P H T INTENDED AS A TEXT BOOK FOR BEGINNERS AND A BOOK OF REFERENCE FOR ADVANCED PHOTOGRAPHERS. BY M. CA_IEY LEA. PHILADELPHIA: BENERMAN & WILSO. 18 68. A P IS Y: e I I e e'e.e~ Entered according to Act of Congress, in the year 1868, by M. CAREY LEA, in the Office of the Clerk of the District Court of the United States in and for the Eastern District of the State of Pennsylvania. PHILAnJrLPHIA: COLLINS, PIIINTER, O5 JAYNE STIIEET I I~ PRE F ACE. IT is intended that this mnanual shall serve both as an introduction to Photography for the beginner, and afford a useful book of reference to those already versed in the subject. Therefore, in the first part will be found brief and simple instructions, intended to enable the beginner to obtain a quick and thorough grasp of the subject. All thlose details which, although of great value to the already skilled photographer, would only confuse the student, have been thrown into the subsequent parts of the volume. The advantage of this arranlgement seemed so great that it was deemed best to adopt it, although it was difficult to avoid occasional repetition in referring a second time to the subjects already treated of in the Introduction. To compress all that it was desirable to say upon a subject now so extended into the compass assigned to this volume, was found extremely difficult. The writer hopes, however, that no serious deficiencies will be found. CO NTENTS. PART I. INTRODUCTION TO PHOTOGRAPHY. PAGE 17 2~ 41 43o CH APTER I. Selection of Materials. II. Making the Negative.. III. Making the Positive.. IV. General Rules for Beginners PART II. PHOTOGRAPHIC OPTICS AND THEORY OF PERSPECTIVE. (CtIAPTER I. General Optics.... II. Of Lenses.... III. Faults incident to Spherical Lenses IV. Focal Lengths of Lenses V. Photographic Objectives.. VI. Photographic Perspective.. PART III. PHOTOGRAPIIlC MANIPULATIONS. C(IAPTEIR I. The Dark Room.. II. The Glass Room..... III. Pyroxyline and Collodioni... IV. The Negative... V. Ambrotypes and Ferrotypes... VI. Portraiture......... VII. Landscape and Architectural Photography. 4 S 52 54 6'i,3 74 94 103 i00, I I ", 126 148 150 161 CONTENTS. CHAPTER VIII. Composition...* IX. On Copying.......... X. The Stereoscope......... XI. Microphotography and Microscopic Photography 1 XII. Development on Paper....... XIII. Silver Printing........ XIV. Failures........... XV. Out-door Photography........ XVI. Dry Plates; manipulations common to all processes. XVII. Dry Processes requiring a Negative Bath 2 XVIII. Dry Processes without a Negative Bath. XIX. Photographic Varnishes....... XX. Treatment of Residues........ XXI. Various Photographic Processes-Transparencies, Enamel ling, etc.2 XXII. Carbon Printing......... PART IV. THEORETICAL CONSIDERATIONS. CJIAPTER I. General Observations..... II. Action of Light on Silver Compounds III. Action of various portions of thie Spectrum. PART V. CHAPTER I. Photography in its Relations to HIealthl II. Chemiical M]anipulations... viii PAGE 174 186 190 192 196 206 228 256 261 274 280 286 289 293 806 312 314 821 . 323 . 828 A MANUAL OF PHOTOGRAPHY. PART I. INTRODUCTION TO PHOTOGRAPHY. CHAPTER I. SELECTION OF MATERIALS. ~1.-Selection of Photographic Lenses. THE first step of the beginner must be to provide himself with the necessary materials for his work; and the choice of his lenses will have much to do with his success. Unless he works with good lenses, his results can never be satisfactory. And further, they must not only be good, but must be such as are suited to the work which he intends to do. Such a thing as a universal lens does not exist. One combination is best for one purpose, another for another. For landscapes the single view lens is the best, that is, it gives more brilliant images than any other. But it has two defects. First, it includes but a small extent of view. This has been remedied by Dallmeyer in his wide angle view lenses, which include a considerable sweep. Secondly, the view lens gives curved lines, that is, lines that are straight in nature are rendered by the view lens slightly curved. So long as there are no architectural objects in the view, this is unimportant, but if such are to be included, then a doublet or triplet must be used. The triplet form of lens is an excellent one for many purposes. It cannot, however, be made to include as large an angle of view as the doublet. The doublet lens exists in very many forms, a description of the most important of which will be found further on. Here 2 INTRODUCTION TO PHOTOGRAPHY. may be cited, only very briefly, the Globe lens, the Zentmayer, the Dallmeyer ("rectilinear"), the Ross doublet, the Steinheil, &c. Of these the globe has been a great favorite with many in this country and elsewhere. I have never shared this opinion, and cannot recommend the lens for any purpose except copying, which it does excellently. Zentmayer's lens gives admirable representations of architectural subjects. Some of the best architectural views -made in this country have been executed with it. It works with too small a stop to be very useful for landscape work. Ross's doublets have been very highly spoken of by good judges, as also Dallmeyer's rectilinear lenses. Both of these inelude a very large angle, with perfectly straight lines. They are well suited for architectural work. For landscape work, then, the photographer will prefer the single view lens and the Dallmeyer triplet, using, when he wants a wide angle, Dallmeyer's "wide-angle" lenses. It may be useful to remark that the additional angle which these last lenses include is accompanied with the disadvantage that (at least to the writer's experience) they curve the lines more than the common form of view lens. Jamin's (now Darlot's) view lenses are very good, and of extraordinary cheapness. The amateur of small means who wishes to take views cannot do better than begin with one or two of them. For portraiture there is but the one form useful, the Petzval objective, commonly known as the "portrait combination," except when groups are wanted to be taken, and where the triplet is proper. Steinheil's new "aplanatic" may also be employed for groups. The portrait combination, though indispensable for portraits, has its utility limited to that one object. If applied to any other purpose whatever, it gives results inferior to those of the other lenses suited for that other work. For copying engravings, plans, maps, &c., any form of lens may be used in which the stop is between the front and back lens, except the portrait combination. To assist, as far as possible, those who may be desirous of accomplishing a variety of work with a limited stock of lenses, it may be said that the lens that comes nearest to being universal is a well-made triplet. It gives excellent views, takes architectural pictures, copies well, and does well for groups, but for por 18 -SELECTION OF MATERIALS. traits it is slow. And as in portraiture it is desirable to require the sitter to sit as little time as possible, this objection is serious. Jamin makes portrait lenses of which one lens unscrews, and may be used as a single view lens. This is a good arrangement, and the lenses, though not always first-rate, can be well recommended, and are very inexpensive. The same maker now makes a so-called "universal" lens, in which a number of separate lenses can be variously combined. Tile orthoscopic lens is a good deal used in Germany, and very good ones were at one time made by Harrison, in New York. This lens copies exceedingly well, and in Germany is much liked for views, but has never become popular elsewhere for that purpose, its pictures having generally a flat effect, and wanting relief. In this respect the large lenses of this sort are generally more objectionable than the small. Further details will be found in Part II., Chap. V. A few words of general advice may be usefully given here to the beginner. Do not make the mistake of beginning with views too small or too large. The smaller the pictures are, the more easily they are taken in every respect; difficulty increases vastly with the dimensions. On the other hand, small prints are apt to be too trifling and insignificant to repay for the trouble expended upon them. Therefore the beginner will do well to start with "half size" plates, and go from that to whole size, after becoming perfectly familiar with all the manipulations. Eventually he will probably prefer to advance to 8 x 10 and perhaps larger work. Generally speaking, the most artistic effects are got with 8 x 10 and 10 x 12 plates. Larger prints are apt to be less pleasing, however technically perfect. It is no advantage whatever to have a lens embrace a very wide angle, except, indeed, where architectural objects have to be taken in positions where the photographer cannot recede beyond a certain point. An angle of 50~ to 60~ is generally best. Lenses should be kept with the greatest care-never wiped with anything except clean soft chamois leather or soft old linen cambric, and even with these only when necessary. The exquisite polish on the surface is of the highest importance, and it is easily injured. 19 INTRODUCTION TO PHOTOGRAPHY. Do not begin by buying second-hand lenses, but go to responsible dealers and purchase the work of makers of reputation. Always use as small a lens for views as will cover satisfactorily the plate. Do not make the mistake of buying, for example, a lens for whole size plates, when you expect to work principally half size, under the impression that the lens will do for occasional use on whole size plates, and for habitual work on half size. So it will; but it will not, for the most part, give as pleasing a picture on the half size plate as the lens made for that size of plate. This is especially to be observed with lenses that cover a small angle. There is less objection to using a wide angle lens for a smaller plate than that for which it is intended, than in the case of a common view lens or a triplet. All makers, even the best, will occasionally, through inadvertence, send out bad lenses. And careless makers will now and then accidentally produce very good ones. In choosing amongst a number of lenses by the same maker, view a piece of perfectly white paper through the lens, holding the latter close to it. If the appearance shows that the glass of which the lens is made has any color, especially if that color be brownish, the lens should be rejected: it may be expected to be slow. So, too, if, when carefully examined by reflected light, it shows any strip, or hair-like lines. Very small bubbles, or white spots, if not exceeding one or two, are unimportant, and often occur in excellent lenses, though, of course, they are better absent. These brief remarks are perhaps as much as the beginner can advantageously act upon. Other points will be explained later. i 2.-Selection of Camera. Without a thoroughly good camera, or box, no first-rate work can be done, and the beginner cannot make a greater mistake than that of purchasing a cheap one. Any camera that is not thoroughly good is absolutely worthless. A camera is to be tested as follows: 1. Observe if all the wood-work is sharply cut and closely fitted. 2. Try the rack and pinion movement, to notice that it works easily and regularly, and not by jerks. 4, 20 SELECTION OF MATERIALS. 3. Rack the back forwards until all the bellows body is closed in; then continue to rack up till the back wood-work just comes into contact with the front. Observe attentively if this contact takes place everywhere at once-top, sides, and corners. If it does not, the camera is worthless, for the sensitive plate will in such a case not occupy a position perpendicular to the optical axis of the instrument. 4. These points having all been found satisfactory, it remains to ascertain whether the sensitive plate, when in place, occupies the exact position of the focussing screen of ground glass. This is the most essential point of all, and is precisely that in which cameras, even of good makers, are apt to be defective. The fault, if it exists, is easily detected with a little attention. Take a piece of plate glass of the size which the dark slide is intended to carry, set it in place, close the door, set the slide on the table, door undermost, and draw out the shutter. Lay across the middle of it a perfectly flat and rigid ruler, a draughtsman's straight edge, or a long, thick, narrow piece of plate glass. Take a piece of smooth hard card, rest one end of it on the plate glass, pressing the side close up to the ruler, and with a sharp hard pencil draw a hair-line where the card touches the ruler. Next repeat this exactly with the focussing slide, ground side of the glass uppermost. If the ca Fig. 1. The bottom of the card A rests on the gla?ss, the side rests against the ruler B C, ai d the penc il line is draw4 where the edge B C touches the card A1. mera is well made, the two hair-lines will exactly coincide to make but one. If they do not, the camera will require to be fitted over again by the maker. Care and attention are necessary to make this trial effectual, but it is essential to make it with every new camera. An absolute coincidence of the two lines must be insisted on. At the same time, the experimenter must be sure that he is doing the measuring correctly, and not producing an apparent discordance by careless manipulation. g 3.-Selection of Stand. For out-door work, a folding tripod is employed. For in-door work rmany forms are in use. Those in which the table is sup 21 v INTRODUCTION TO PHOTOGRAPHY. ported by a single cylindrical stern are very objectionable, for want of steadiness. The most absolute steadiness is requisite, and a large proportion of the stands in the market fail to fulfil this requirement. A stand cannot be judged if almost unloaded. Place a heavy camera on it, strike it a gentle blow, and observe if any vibration follows. ~ 4. -Selection of Chemicals. Few photographers have sufficient chemical knowledge to be able to apply tests of purity to their chemicals. Perhaps the very best advice that can be given to a beginner is to observe who amongst his friends is most regularly and completely successful, and then to obtain materials from the same place. In fact, the demands of photography are now so enormous, that good materials can be obtained almost anywhere. The substance most likely to give trouble, in the hands of a learner, is nitrate of silver. This last should always be purchased prepared expressly for photography-never from the druggist. Without the best and purest neutral nitrate, the negative bath cannot be expected to work well. ~ 5.-Selection of Glass for Negatives. Of all matters connected with photography, this is that which is most habitually overlooked. Plc,te glass has some evident advantages over blown. Its surface is a true plane; the material of which it is made is generally whiter, and it is free from blebs and other faults and irregularities. On the other hand, it has been asserted lately that the artificial surface of the plate glass, produced by polishing, does not hold the collodion and varnish so well after a lapse of years as the natural surface of the blown, and that with time the film is more apt to crack and suffer. In consequence of the high price of plate glass in America, blown glass is almost exclusively used. But in this blown glass there is great variety of quality. 1. Some is much greener than other. A strong green color tends to considerably lengthen the time required for printing from the negative: this is always an objection. 2. Glass varies greatly in t[ic7?ne,ss. It is a great advantage 22 MAKING THE NEGATIVE. to have stout glass; the loss from breakage of negatives in the printing-framnes is less, and the operator may venture to apply a strong pressure in his frames where his glass is strong: he thereby gets a sharper and cleaner print. 3. Blown glass varies extremely in curvature. Much of it is very flat; much, again, greatly curved. All that is not very nearly flat should be rejected. To give some idea of the amount of curvature allowable, place a straight edge so that the two ends of the piece of glass shall touch it, and observe what distance the middle of the plate is from the straight edge. It may be said that where this distance exceeds J'6 of an inch in a plate of 6', x 82, it should be rejected as unfit for photographic purposes. Because, first, the centre of the plate will not coincide with the position of the focussing screen. An error not exceeding As of an inch is to some extent corrected by the pressure of the spring in the dark slide (the plate must invariably be collodionized on the concave or hollow face), and the error is thereby reduced. Secoindly, glass that has any, but a very slight, curvature, runs a much greater risk of breaking in the printing-frame. CHIIAPTER II. MAKING THE NEGATIVE. , 1.-Absolute Cleanliness. ALL photographic work depends upon the delicate turning of nicely-balanced affinities, which a slight alteration of the conlditions may completely reverse. It is necessary, therefore, that the operator should not only follow closely the directions given, but that he should learn to constantly maintain a perfect cleanliness. All the vessels which he uses must be irreproachably clean; and, as far as practicable, each should be restricted to some particular use, so that if slight vestiges of substances escape the attention, such may be less hurtful. The hands, especially, must be constantly washed; there is no way in which small portions of material are so readily transferred as by adhesion to the fingers. 23 INTRODUCTION TO PHOTOGRAPHY. In all these respects too much precaution cannot be taken, and many failures, perfectly unaccountable to the beginner, may be traced to trifling neglects of this sort. , 2.-Preparing the Glass. Unless the glass be perfectly clean, a regular development cannot be hoped for. Perhaps the best method of cleaning glass is one introduced into photography by the writer a few years since, and which has since been extensively used. Provide a large glass pan, into which make a mixture in the following proportions: Bichromate of potash........1 ounce. Sulphuric acid........ 1 fluidounce. Water............. 15 fluidounces. Place the pieces of glass in the pan alternately, one at each end, so that their sides shall overlap a little, and allow the free passage of fluid between them. Pour on the above mixture. For new glass a day will be sufficient to destroy the greasiness. Old glass that has been used before, especially if it has been varnished, will require two to three days, or a mixture containing only half the above proportion of water. So long as this bath is yellowish-brown, it is active. -When it acquires a violet color, it is spent, and will want renewing. After soaking in this bath the glasses will require no washing, but should be placed in a trough or other convenient vessel under a tap of water for ten or fifteen minutes. Then take them out one by one, let the water run a few ioments on each side, and then rub dry with soft blotting-paper-not with cotton rags, as so universally directed. Cloths always leave fluft, which has to be carefully brushed away afterwards-paper does not. It is necessary to roughen the edges of the glass with a coarse file. The film is less likely to slip offt; and the hands are less apt to be cut. A coarse file is to be drawn two or three times along each edge; of course, it is only needful to do this on the edges of the concave or hollow side, as this is the one which invariably receives the collodion. The roughing should precede the cleaning. After cleaning the glass must be handled as little as possible; its face must never- be touched by a finger, or there will probably be a finger mark developed on the negative. Clean glass should be 24 MAKING THE NEGATIVE. rolled up in clean paper, and set in a box kept out of the reach of dust and vapors. Nitric acid may be used for cleaning, or caustic alklali; but the above is not only the easiest and most economical, but is perhaps the only one with which an old picture never reappears on the development of a new one. ~ 3.-The Negative Bath. Of all that the photographer works with, nothling exceeds in importance the negative bath. Its preparation is exceedingly easy, and, if thoroughly good nitrate of silver be used, it cannot fail to work well, if no mistake or oversight has been made in its preparation. A verlicau Igass bath is to be procured; there is none other which is perfectly safe. In a porcelain bath, if there is the slightest flaw in the glazing inside, the solution will penetrate it, and gradually saturate the whole of the porous biscuit which makes the body of the vessel, between the inside and outside glazing. This not only involves a great loss of expensive silver solution, but after a time the outside glazing also probably cracks, and some day the operator finds his bath empty. In many cases porcelain baths last for years, but there is never a certainty about them, as there is with glass. The "photographic ware" has been much complained of in the same way. A "whole-size" bath, for plates 62 x 8-, will be found a convenient one for the beginner, as, even if much smaller plates are worked with, it is not worth while to use a smaller bath-it holds too little solution and changes too rapidly. The "whole-size" baths require about 2o ounces of solution to charge them. This solution is to be made as follows: Dissolve 2 ounces of nitrate of silver in 25 ounces of water, whIich need not be distilled water. Leave the solution in a glass bottle in the sunlight for several hours, or in cloudy weather for a day or two near a southerly window. Separate this into two equal portions. Take 3 grains of iodide of potassium or iodide of ammonium, dissolve it in a few drops of water, and pour it into one of the halves; stir up well and let stand one-half an hour, or longer. Filter the other At,cagf into a clean bottle, and then filter 25 INTRODUCTION TO PHOTOGRAPHY. into it the second half, that to which the iodide of potassium was added. Observe: The two portions are not to be mixed until afler they are filtered, and the portion to which the iodide was added is to be filtered last, if the same filter be used for both. Next, take a clean six-ounee stoppered vial; place in it one fiuidrachm of pure nitric acid, fill it up with water, and label it "Dilute nitric acid, ten minims to the ounce." To the twenty-five ounce bath add one fluidrachm of this dilute acid. This will probably be enough; but if the bath gives a foggy picture, you may add another fluidrachm, remembering, however, that the 7ess nitric acid oadded, the more sensitive your _plates will be. In summer more acid will be required than in winter to get clean plates and keep off fog. The negative bath should always be kept covered to exclude dust and dirt. Constant care must be taken to let no extraneous matter get into it, and to place it in nothing, and nothing in it, that is not pe)fectly clean. ~ 4.-The Developer. Mlake the developer as follows: Proto-sulphate of iron Acetic acid, No. 8 Alcohol.. Water.. The developer, if kept corked, will keep for a couple of months. It is ready for use as soon as the solution of the sulphate of iron is complete and the whole has been filtered. As it grows older it becomes reddish, but so long as kept clear by filtration, the reddening is rather beneficial than otherwise. ~ 5.-Collodionizing the Plate. iHolding the clean glass plate by pressing a finger or two of each hand at the edges of the plate (the fingers must never touch the face), hold it up to the light, and look along the long edge to see which is the hollow or concave side, as that is invariably the one which is to receive the collodion. Next brush it off with a broad soft camel's hair brush, which must be kept clean and free from dust, and be used for no other purpose. 26 . 450 grains. 2 1-L ounce. 1 -L 4 c 2 . 20 ounces. MAKING THIE NEGATIVE. Hold the plate in your left hand, three fingers supporting it underneath, your thumb pressing on the corner, and the narrow end towards you. It is a good plan to fold up a piece of blotting paper, and put it between the bottom of the plate and the finger ends. For want of this there will occasionally appear curious mottled markings at the points where the fingers touch the under side. Take the collodion bottle in your right hand, having previously removed the cork and wiped the lip Fig. 2. to remove dust or fragments of dried collodion. (Never neglect this.) Pour the collodion slowly and steadily on, A letting it come upon the plate at a spot a little further from you than the middle-say equidistant from the end and the two sides. Pour on till the pool covers rather less than half the plate. - 4 Incline the plate so that the pool may ex- Hold at 3, pour on at A, and off at 4. tend itself to corner No. 1, then to corner No. t. 2, next to corner No. 3, where the thumb is, and then to No. 4, at which you pour off the excess. This is all to be done quite coolly, and yet without loss of time. The collodion must go up futll to the edge of the plate all round, and with a little practice this is accomplished with great ease and without spilling a drop. It is best not to pour back the collodion into the bottle from which it came, but have a separate bottle ready, uncorked. The operation of pouring off requires the operator's best attention. The plate must be slanted but very little, otherwise the collodion runs off too fast, and leaves too thin a film, especially at corner No. 1. At the same time the operator rocks the luate, that is, turns it backwards and forwards, one quarter round, without changing the inclination. If this be neglected, the film will be full of crapy lines. If the plate be properly rocked, it will dry as smooth as the glass itself. I have endeavored here to give as clear a description of the method of collodionizing a plate as possible; at the same time it is unquestionably one of those manipulations which it is almost necessary to see done, in order to execute properly one's self. I do not give here any formula for making collodion. I stren 27 INTRODUCTION TO PHOTOGRAPHY. nously advise the beginner to introduce no unnecessary difficulty by such attempts, but to procure a reliable collodion from some professional photographer or trustworthy dealer. When he has mastered the manipulations, he may advantageously make his own collodion, for which a number of good formulas will be given further on. The nitrate bath, the developer, and the fixing solution, on the other hand, every one must learn to prepare for himself from the outset. f 6.-Sensitizing. The collodion coating quickly sets-in half a minute or less in summer, whilst a minute may be necessary in winter. Its condition is commonly judged of by gently touching it near corner No. 4 with the tip of the finger; if the film does not wet the finger, but receives a slight depression from it, which remains after the finger is removed, it is called "tackly," and is now ready for immersion in the bath. Up to this tihe the rocking motion is to be steadily continued, pausing only for a second, if necessary, to ascertain the condition of the film. Wheni this has attained the proper state of setting, the plate is to be rested upon the dipper firmly and steadily. The operator next lowers the dipper, carrying the plate with it, into the bath, by a gentle, continuous, and uninterrupted motion. For if he pauses for any fraction of time, however short, the part of the film which at that moment corresponded with the surface of the bath will show a distinct line, ruining the negative. No unnecessary delay should occur in putting the plate in the bath, or the risk of marbled stains is increased. Dippers are made of porcelain, glass, and gutta-percha. If glass ones could be got of a right pattern, they would be preferable, but made of rods they are too fragile. The porcelain are good and the gutta-percha also, provided they are well made, and consist wholly of gutta-percha, without any metallic support in the centre. The porcelain dipper may rest in the bath when not in use; the gutta-percha dipper must never be left in the bath. The beginner is advised to use the porcelain. The plate having been placed in the bath will be left quiet for a couple of minutes, and then must be moved up and down from time to time; and a side motion is also beneficial, especially if the plates show a tendency to form lines in the direction of the dip, a 28 MAKING THE NEGATIVE. trouble of which much complaint has been made by some photographers, though it has never been experienced by the writer. Until the plate has been in some minutes it should not be raised in moving so as to be partly uncovered by the silver solution. The time requisite for stay in the bath cannot be fixed in minutes with any positiveness, as it depends somewhat on the temperature, the nature of the collodion, and the condition of the bath. From three to five minutes is about the time. The plate is ready when, on withdrawing from the bath, no oily lines form on the surface, but the whole face presents a uniform moist film. The plate should never be left longer than necessary in the bath, as by so doing the film tends to dissolve, thus choking the bath with excess of iodide, and rendering the plate irregular. Worse still, there is a great tendency in such plates to give flat and dull images, at least in collodion containing bromides. The plate is now to be removed from the bath and rested on several thicknesses of soft blotting-paper, changing its position every few seconds, until it no longer wets the paper. A thorough draining in this way is very important, and cannot be neglected without danger of streaks and other irregular action. At the same time the back of the plate is to be carefully wiped dry with soft paper. It is a very good plan to keep ready pieces of thick soft red blotting paper, half an inch smaller than the plate all round; and after it has been wiped clean to apply one of these pieces moist, but not too wet, to the back. This precaution, though recommendable, has not yet come into general employment. Its use is to diminish internal reflections, as will be more fully explained hereafter. In all these operations the face of the plate must never be touched by the fingers, and with the same precaution the plate is to be lifted and gently set into its place in the dark slide, taking care that the shutter is in its place. The door is then closed. From the time that the plate is lifted from the bath the same edge must carefully be kept undermost; that is, the side which went undermost into the bath must be kept undermost-must be that which rests on the blotting.paper-must be kept undermost in the transfer to the dark slide, and the slide with its plate in it must be carefully kept with that edge downwards, not only during exposure, but in carrying backwards and forwards and up to the moment of development. This is e8sentica; neglect of it will 29 INTRODUCTION TO PHOTOGRAPHY. almost certainly result in streaky lines and irregular deposits along the outside of the plate, running up in places some distance into the plate. If the small size of the bath renders it necessary to set the plate in end down, when the side is to be down in the slide, the plate must be turned immrediately on taking it from the bath, and the draining and blotting done whilst it is in the same position which it is to have in the slide. Particular descriptions of the dark room and glass room must be omitted for the present. Here it is sufficient to say that all the operations of sensitizing and developing must be performed by yellow light. A very simple way of converting an ordinary room into a dark room for photographic work consists in procuring some of the very thickest and stoutest brown paper made for envelopes, and pasting pieces of it over the panes of the window; a great deal of light will come through this, sufficient for all the operations, and yet, if the paper be good and thick and of fine grain and quality, there will be no danger of fogging. If, however, the sun shines directly, at times of the day, upon the window, it will be well to have a buff curtain on rollers inside the window, so that when the light is too strong it may be properly tempered. If the room used as a dark room has two windows, it will be found preferable to cover the panes of one only, and to have closely fitting inside shutters to the other, over the joints of which black muslin must be pasted or tacked. In this way the room may be lighted at any moment, and may serve for other uses than merely as a dark room. However the dark room be arranged, provision must be rnace for its thorough ventilation, the fumes of collodion being exceedingly depressing to the nervous system, and tending to undermine the health. This subject will be recurred to hereafter; it should never be lost sight of by the photographer who values his health. , 7.-Pocussing. If the photographer has not done his focussing beforehand, he may do it while his plate is in the bath, and should never, if possible, delay it until the plate is in the slide and waiting. As a general thing, the less time that elapses between the placing of the plate in the dark slide and the taking it out to develop, the greater will be the chance of a good negative. 30 MAKING THE NEGATIVE. Throwing an ample black cloth over the camera, and placing his head beneath it, the photographer proceeds to take his focus. Few persons have unassisted sight so sharp as to enable them to take a thoroughly good focus, although a delusion to the contrary is very wide-spread. It is always better to examine the image on the ground glass through a microscope, as a better focus can be got more quickly, and with less strain upon the eyes. The microscope should consist of two lenses in the same cylinder, at least an inch in diameter. The difference of fatigue to the eyes in using large and small lenses is enormous. A magnifier, with lenses of one and a half to two inches in diameter is the best; its expense is small, as it is not absolutely necessary that the lenses should be achromatized. The little doublets used by engravers are good, and larger ones can be got of any optician of the same pattern. The writer does not advise the system of focussing on clear glass with an adjusted eye-piece. The operator is not to take his focus on any point of the picture indifferently, but according to the following rules: In taking a single portrait, focus on the face as the most important point. In taking two heads equidistant from the centre, focus on either head, not on any more central object. In taking a group, focus on one of the heads occupying a position midway between the centre and the extremity of the group. In focussing a landscape, focus on the foreground at a point midway between the centre and the edge of the plate. These directions are important, and cannot be disregarded with impunity. Careless focussing is almost the worst fault that a photographer can have, and will counteract every care or precaution that he can take in other parts of the process. g 8.-Exxposure. The time of exposure for a wet plate may vary from a fraction of a second to half an hour. With a portrait combination, medium stop, and good light, from five to fifteen seconds, or even more, may be required. With landscapes, taken by a view or a triplet lens and medium stop, from ten seconds up to several minutes may be given, according to the light. With a bright light, and by having the chemicals in exact order, a picture may be got in a fraction of a 31 INTRODUCTION TO PHOTOGRAPHIY. second with a short focus lens, using a large stop. The operator, however, will do well to leave instantaneous photography until he succeeds regularly and without difficulty in ordinary expo sures. The slide should always be set into the camera steadily and gently, not with a jerk or snap, lest any dust be set in motion and settle on the sensitized plate, the result of which will be seen in comets or poin-holes. Q 9.-Development and Redevelopment. The operator brings back his dark slide, without loss of time, to the dark room, never forgetting for an instant to keep that part of the slide down which was lowest in the camera, and in all previous stages. Holding the slide with the left-hand edge in his left hand, he opens the door with his right, places his thumb on the upper edge of the plate with the fingers touching it lower down, and, by inclining the slide a little backwards, brings out the plate. This is now transferred to the left hand, always keeping the lower edge downwards. He now turns the plate up nearly to a horizontal position; a proper quantity of the developer (about an ounce for a whole-sized plate, or, for a beginner, a little more) has previously been placed in a suitable vessel-Fig. 3 represents a good shape; this the operator takes Fg 3 in his right hand, and, holding it a little inclined, and <~_~ at the upper edge of the plate near the left hand, pours out the liquid, at the same time drawing the vessel towards the right, so that the liquid may spread rapidly and evenly over the whole surface of the plate. Some dexterity is required to do this, except with very small plates. Just as the developer spreads over the plate and reaches the lower edge, the plate is carried to a horizontal position, for it is an object not to let more than can be helped run over. The developer becomes mixed on the surface of the plate with the bath solution with which the film is impregnated, and this mixture provokes the development. If a portion is wasted by washing over the side, the image will come out less strong, and a redevelopment will be more likely to be necessary. The rapidity of development under the action of the developer 32 MAKING THE NEGATIVE. will depend on the exposure. If the picture flashes up instantly, the exposure has been too long, and the picture will want contrast. If the picture comes out slowly, reluctantly, so that after a minute or two only the strongest marked points of the subject are visible, the exposure has been too short, and the picture will probably be too full of contrast, wanting in detail, and hard and blocky. If the picture soon begins to show itself, and instead of flashing out suddenly, grows steadily and even rapidly in strength, a good result may be anticipated. As the development goes on the operator inclines the plate in different directions, so as to keep the developer in a state of constant motion, thereby rendering its action regular and even. When the plate has reached, or nearly reached the desired strength, the operator pours off the developer from one corner into its vessel again, and as he drains the last drop, he raises the plate perpendicularly between himself and the light, and judges of its strength and character. If these appear satisfactory, he stops the operation by washing off the plate; if not, he pours on the developer again (provided this last has remained active and clear), and keeps it on a few moments longer. B3ut if it seems to have ceased its effects, and still more, if the slightest tendency to fog manifests itself, or if the developer looks in the least muddy, the operator quickly washes the plate, and if on a further careful inspection he finds that it still wants strength, he proceeds to redevelop. Redevelopment may be done either before or after fixing, the difference is but-very slight in the final result; as far as it goes, it may be stated as follows: If the contrasts are likely to be a little too great, or tend that way, redevelop before fixing; if the contrasts are scarcely sufficient, fix first and redevelop afterwards. Not much, however, in the way of a curative agency can be expected in this way, and pictures which are either too harsh or too uniform, are best wiped out at once and taken over. The operator will always bear in mind, in deciding when his development or redevelopment is carried far enough, that the apparent strength of the picture, as he then sees it, will be considerably reduced in the operation of fixing, and for this he must make due allowance. Negatives that come out of the right strength by the first development are the best. If under-exposed, they are apt to become hard and crude in the process of redevelopment; and if over 3 33 INTRODUCTION TO PHOTOGRAPHY. exposed, the evil is incurable. A brilliant print can only be got from a brilliant negative. Redevelopment may be effected in various ways. The most usual is with pyrogallic acid, and that is the plan which I shall here describe. To redevelop with pyrogallic acid, the operator keeps in a stoppered vial the following solution: . 60 grains. . 120 IO'e 6 ounces. Nitrate of silver Citric acid Water.. This mixture keeps for months. When the iron development has done what it can, and before any disposition to fog sets in, the plate is to be washed off. In a convenient developing vessel the operator puts water, about an ounce or a little less for a 621 x 81 plate, and proportionately for other sizes. HIe next adds a little pyro, about two grains for the ounce of water, in which it immediately dissolves. He then adds a few drops, say fifteen or twenty, of the silver and citric acid solution to the ounce of water, and pours the mixture over the plate. The image immediately begins to grow in strength, and, by keeping the silver and pyro on, any desired degree of strength can be obtained. The redeveloper soon darkens to a wine color, and in that condition its action is still powerful. But if it becomes in the least muddy, it must be rapidly washed off the plate. So long as the solution remains transparent and bright, even if port-wine color, it is not easy to fog the picture. Still, even the pyrogallic developer is not to be trusted too far, or fog may set in in brown spots. A pyrogallic development may be used in the first place instead of the iron. In this case the pyrogallic acid is simply dissolved in water, about a grain to the ounce, a little acetic acid is added, and the mixture is poured over the plate as it leaves the frame. This is a very easy development, and gives bright, strong pictures. But the preliminary development with iron is preferable, because softer pictures are got, and more full of detail. Pyrogallic acid cannot be advantageously left in solution in water, as it spoils. If preferred, it may be kept dissolved in alcohol, sixty grains to the ounce, when ten or twelve drops will be equal to one grain of the crystallized acid. The vessels used for developing must be kept scrupulously clean. If the remains of the developer be left in them a few 34 MAKING THE NEGATIVE, minutes, it becomes turbid, and a gray-black precipitate of metallic silver collects round the sides and bottom. Any of this left in will tend to render the next lot of developer muddy, and therefore must be completely removed. I am in the habit of keeping beside me the following solution in a beaker or wide-mouthed bottle: Concent. solution bichromate of potash Sulphuric, or better, hydrochloric acid Water....... . I fluidounce . is .3 fluidounces. It is only necessary to pour this solution into the dirtiest develo6ping vessel, and then immediately out again, when it will be found perfectly bright and clean. It is scarcely necessary to say that it must be well rinsed. The same solution is very useful for removing silver stains from the fingers. If got into cuts or abrasions of the skin, it is to some violently irritating, to others quite indifierent, except a momentary smarting. It is much preferable to the use of cyanide of potassium, a most dangerous chemical, and the indiscreet use of which is injurious to health and may become destructive to life. Perchlorcide of iron may also be used for cleaning the fingers. Or they may be rubbed with strong tincture of iodine (alcohol 1 oz., iodine 40 grs.); and when the stain has become yellow (not before), it will dissolve in a strong solution of hyposulphite of soda. Of these methods, the first will generally prove the most efficacious. All silver stains, however, should be attacked before they are set by exposure to light, otherwise the difficulty of getting rid of them is greatly increased. 10.-]Fixing and Drying. The negative fixing-bath consists of a strong solution of hyposulphiite of soda, in the proportion of five or six ounces to the pint of water. Some pour the solution over the plate until it is clear. But this involves a loss of time. It is better to keep the fixing-bath in a horizontal pan, and carefully to slide the negative into it. When the yellow opaque appearance of the iodide and bromide has completely disappeared, the plate is fixed. The same bath may be used for a number of negatives, but should not be kept too long. 35 INTRODUCTION TO PHIOTOGRAPHY. The plate thus fixed is to be set under a tap and thoroughly washed by allowing a stream of water to fall upon it, whilst the plate is supported at such an angle that the ripple is seen to spread in all directions, and keep the water in continual motion over the whole surface of the plate. Ten to fifteen minutes is the right time for washing a negative, although much less is often given by hasty operators. It is almost as important to wash the back as the face, although the latter requires only simple rinsing off. If this be neglected, portions of the hyposulphite bath will remain there, and, when the plate is set up to dry, will run down to the edge, and thence be drawn up by capillary attraction into the film, preparing the way for spots and stains at some future time. The plates are next allowed to dry, either reared up corner-wise in a drying-frame, or simply supported in a vertical position, resting on several thicknesses of blotting-paper. From the time that the developer is thoroughly washed off, the plate may be exposed to the light without injury. But it is usually mnore convenient to fix in the dark room, though this is not really necessary. If it is intended to redevelop the plate after instead of before fixing, the wash-ing must be equally careful after the fixing solution is applied, or the application of the redeveloping solution will cause brown stains. g 11.-Varnishing the Negative. To varnish a negative well will require both care and attention on the part of the beginner, until by habit and practice a complete control over the operation is obtained. Choice of Vornish.-First as to the selection of varnish. The beginner should never attempt to make his own, but always procure a reliable commercial varnish. The experienced photographer should always make, never buy; not so much for economy, though the saving is material, but in order to be certain that he has exactly what he wants-a hard, tough varnish, made out of the very best materials. Suitable directions will be found in the latter part of this manual for preparing negative varnishes. The commercial varnishes may be divided into two classesthe benzine and the spirit varnishes. The former will mostly dry clear, even if used cold; the latter always require the aid of heat. On the other hand, the benzine varnishes (so far as my 36 MAKING THE NEGATIVE. experience goes) always reduce the strength of the negative considerably, whilst the spirit varnishes do not; and it is thought that the latter are more durable. A beginner can, perhaps, learn more easily on a benzine varnish, but the writer considers the spirit varnishes preferable on account of their acting less upon the density of the negative. The two different sorts can always be distinguished by the odor. Ap)plying the Varnish.-First dust off the plate, either very gently with a very soft, broad camel's-hair brush, or by blowing with a bellows. With plates developed with iron, or redeveloped, the latter is the better plan. To apply a spirit varnish, warm the plate either by a stove or over a Bunsen burner, or on a tin vessel filled with hot water. Try the temperature by holding it at one corner with the left hand, and moving the right hand under it and applying the side of the hand and back of thumb to various places to see if the heat be uniform. To be right, the temperature should just be pleasant, not feeling hot. If too hot, set aside a few minutes to cool. If used too hot, there is danger of getting lines, as will be presently described. If used too cool, the varnish will probably "dry dead." A benzine varnish requires no heat except in damp weather. Pour on the varnish, holding the plate at the left corner, with the narrow side next you. Begin at the distance of an inch and a half to two inches (for a whole plate, proportionately for other sizes) from the far end, and midway between the corners. Whilst you are pouring, incline so as to get it down first to one corner, then to the other. Then having put on a liberal supply, slant the plate towards you and bring the pool of varnish towards you, in a full, slow wave, keep its border as square as possible, making it advance slowly and quietly; if one edge gets a little the advance, incline the plate the other way to bring it up. With too little varnish or too much tilt to the plate, long arms will start out, and whilst you are slanting the plate this way and that to get it covered on some part of the border, the wave will stop moving, and a line may result. Having now got the whole plate covered, keep it quite level, or even tilt it backward, so as to send a returning wave clear up to far end of the plate. The varnish should rest on the whole plate five or six seconds before beginning to pour off; otherwise it will not soak in sufficiently, and so dry Wea& 37 INTRODUCTION TO PHIOTOGRAPHY. Having let it soak in sufficiently, incline it very little, so that it will run off at the right-hand near corner into the "pouring-off bottle" held there to receive it. After it has run slowly for three or four seconds, the plate being of course nearly level, bring it suddenly up by a quick mnovement til it is vertical, and there hold it perfectly still for half a minute or more that it may set. If moved at all short of this time, ridges may be expected. Some varnishes require no more heat than the first application. Many, however, should be dried by heat, as well as be applied on a warm plate. If so, hold the plate exactly in the position that it drained off vertically, and bring it with its face within a couple of inches of a hot stove. The main points are to get the corners covered immediately after you begin to pour, to put on enough, or to bring it down as above explained to afull, slow, sludre wave. The learner cannot pay too close an attention to these directions. By doing so he will get a smooth, even plate. Neglecting them, he will find: Ridges.-These start from some point at the edge of the plate and extend some distance over the face of, or even all across the negative. If strong enough to show in printing (they show less, of course, by printing in the strade than in sunlight), there is nothing but to remove the varnish and revarnish, a most disagreeable operation, and worse than half a dozen careful varnishings. Lines result from a momentary stopping of the wave of varnish. The varnish dries a little on the hot plate during the pause, and the result is a line exactly marking the position it then had. The hotter the plate, the more apt lines will be to appear. If a line has been made and is seen before you begin to pour off, it may be lessened, and sometimes entirely removed, by keeping on the varnish a few seconds longer than usual before beginning to pour off. I)Drying Dead. -This results in the production of a film looking like ground glass-sometimes fine, sometimes coarse. If fine, it may scarcely show in the printing; if coarse, it will. This may arise from several sources: From dampness of the Film.-After the film is surface dry, it takes a long time to dry through, and the drying must be thorough before the varnish is applied. So, too, the film is very absorbent of atmospheric moisture, and even after thorough drying and 35 ~MAKING THE NEGATIVE. standing for weeks, may easily in damp weather absorb enough to affect the varnishing. It is therefore better, so far as convenient, to varnish in clear dry weather, or at least after the plate has remained some time in a warm dry room. Too thin a varnish may also cause drying dead, or too little applied. If, as soon as the plate is covered, the varnish be poured off again, it will almost certainly dry dead, because the surface only was moistened; this presently soaks in and leaves the film only half saturated with varnish. Breathing on the plate may at times, and under some circumstances, lead to spots of deadness. A close attention to the above directions and a reasonable experience will enable the photographer to get through his varnishing with rapidity and certainty. But if the varnishing is defective, it must be removed and done over. For this purpose the plate is to be laid in a flat pan, film side up, and covered with alcohol in the case of a spirit varnish, and benzine for a benzine varnish. Mover it up and leave for an hour or two, or till the varnish is pretty well dissolved. Wash off with clean alcohol, dry, and re-varnish. The operation is unsatisfactory, and generally as much trouble as taking a new plate. The solution and removal of the varnish are rarely perfect, a whitish substance being left behind, which, however, mostly disappears by the new varnishing. When it is intended to print a very large number of positives from one negative, two coats of varnish may be applied. Mr. G. W. Wilson, whose stereoscopic work is so remarkable, always gives two coats, touching out defects between the two. He also warms and dries his plates beside a fire in a grate even in midsummer. It is a good plan, as soon as the face of the varnished plate is dry, to draw a piece of blotting-paper along the lower edge of the glass; this prevents the production of a thick ridge there, which would have a tendency to lift up the paper in printing, and pre vent a close contact with the adjoining parts. ~ 12.-Ambrotypes and FPerrotypes. The ambrotype is a thin negative taken on glass, the ferrotype on thin iron varnished. The exposure must be much shorter than 39 INTRODUCTION TO PHOTOGRAPHY. for negatives, the bath a very little more acid, the collodion thoroughly ripe. Develop only till the details appear, and then wash immediately and fix in hyposulphite. An ordinary negative collodion may be used if it is thoroughly ripe; if not, tincture of iodine may be added till it is sherry wine colored. (Tincture of iodine may be purchased, or may be made by dissolving iodine in alcohol. Forty grains of iodine to the ounce of alcohol is a convenient strength.) Some photographers prefer a special collodion containing iodide of potassium, now never used in negative collodions. Mr. Thomas, of New York, uses the following proportions:- - Iodide of potassium.......... 50 grains. Bromide of potassium......... 30 " Dissolve these salts in 3 ounces of alcohol. Take 60 grains of pyroxyline, dissolve it in 5 ounces of ether and 2 of alcohol. Then add the above. The developer is to be the saine as for negatives, taking care that it be sufficiently acidified, for which purpose one-half more acetic acid may be added than for negatives. ~ 13.-General Remarks. Avoid doing anything which may cause dust in the dark room. Keep the dark slide clean and well wiped. Notice the camera from time to time to assure yourself that the wood work is close and tight. See that the focussing slide sits tight and close up. The springs that hold it to the body of the camera will sometimes get out of order and affect the two slides differently, so that one comes up more closely than the other. The result of this will be that the focussing surface no longer corresponds with the sensitive film, and no matter how carefully the focussing be done, the pictures will not be accurately sharp. Make sure that the camera-stand is absolutely steady and not given to trembling. See that the dark room is thoroughly ventilated, so that whilst at work you are not inhaling noxious vapors, and as little as possible of the fumes of collodion. 40 MAKING THE POSITIVE. CHAPTER III. MAKING THE POSITIVE. 1 1.-Sensitizing and Printing. WE shall here only describe the proceeding with albumenized paper, now almost exclusively used. The process on plain paper will be described elsewhere. Manly excellent qualities of albumenized paper are to be found in the market. The sheets are to be cut up into convenient sizes, and one corner is to be folded backwards for half an inch or threequarters. The piece is then held at its two ends, is folded into a loop by bringing the hands somewhat together so that the centre will be lowest, and the albumenized surface undermost. The centre of the sheet is made to touch the bath first, and then, by opening the hands and lowering them, the whole surface is regularly opened out on the bath. In this way air-bubbles are avoided. Should an air-bubble remain under the paper, its place will be marked by a white spot in the print. Positive Bath. Water....... Nitrate of silver.... The paper remains on it about four minutes in winter, and two to three in summer. It is then lifted off by the corner turned up, and pinned to a rod or string to dry. A convenient method is to take a long strip of wood, and glue on it at spaces corks, into which to stick the pins. When the bath turns dark, shake it up with half an ounce of kaolin, or add to it ten grains of citric acid dissolved in a little water. Let it stand some hours, with occasional shaking, and filter. Examine the bath from time to time with red and blue litmus paper, and keep it as nearly neutral as possible. If the blue litmus turns red, the bath is too acid, and may be neutralized .41 . 22 ounces. 3 4 4 INTRODUCTION TO PHOTOGRAPHY. with a grain or two of bicarbonate of sodium. If red litmus paper turns blue, the bath is alkaline, and a little dilute nitric acid must be carefully added. It is best to have the solution an inch deep in the glass or porcelain bath. Too shallow a bath tends to irregular action. See that the paper is thoroughly dry before printing it. A dense negative prints best in the sun, a thin one in the shade. That is, it is to be exposed at a window to a good light, but not to sunshine. Print till the highest lights ast begin to color. By this time the dark shadows ought to show the greenish, almost metallic, look known as "bronzing." Examine the print from time to time, taking the frame to a darker part of the room, open the back gently, taking care not to shift the print, bend it back, and judge of the degree to which the printing has gone. As fast as the exposure is finished, throw the prints into a dark drawer. When all are ready, proceed to wash them by putting them one by one into a basin of water, where they lie ten minutes. This water is to be carefully added to the residues, as it is rich in silver. Change two or three times, then tone. As the printing-bath will continually lose in strength, it should be kept up by adding crystals of nitrate of silver. g 2.-Toning Bath. .. 16 ounces. .4 grains. .1 ounce. In five or six hours it will be ready for use. In very cold weather, a little more gold must be used; and the bath, except in hot weather, should be warmed till it is tepid. Put in only a few prints at a time, and keep them constantly moving about. When they reach the shade you prefer, let them remain a little longer, as they will afterwards recede a little in color; then take them out, pass them through clean water, and proceed to fixing. Prints that look blue when finished, have been over-toned by too long an immersion. 42 Water. Chloride of gold. Acetate of sodium MAKING THE POSITIVE. ~ 3.-Pixing Bath. Water...... Hiyposulphite of sodium. Keep the prints moving about in this, and leave them in fifteen minutes. The above bath will suffice for two whole sheets, and must be increased in proportion if more are to be toned. Never use on any subsequent day a bath that has had even only one single printfixed in it, or the print so toned will surely fade. ~ 4.-Washing. A very thorough washing is needed to prevent fading. Prints thrown into a tank into which a tolerable stream of moving water falls, will be sufficiently washed in six to ten hours, provided there are not too many of themn. When the number is large, the tank must be continually emptied of water and refilLed. CHAPTER IV. A FEW GENERAL RULES FOR BEGINNERS. 1. INVARIABLY wash the fingers under the tap immediately after they have been in any solution, but most particularly after hyposuIphite. By neglecting this you will transfer portions of one solution to another, and lay the foundation of long series of failures, which may prove utterly distressing and perplexing. 2. Do not have the ambition to commence with difficult work. Point the camera out of the window, and take the view, such as it is, until you can do it with certainty and success. After that will be time enough to try portraiture-last of all, copying. 3. Begin with small plates, and do not try large ones until you have mastered the smaller. Half-size will be the largest proper to begin with. 4. Do not undertake to. make collodion before you have learned how to use it. Be satisfied to purchase that which some experienced friend recommends. 5. Do not tend towards intensifying thin pictures by after 43 . 32 ounces. 4 4 4 INTRODUCTION TO PHOTOGRAPHY. treatments. When photography was less understood this was oftener necessary. It is better to wash off and begin again, and generally less trouble to get a better result. 6. The quickest way to learn is this: take any simple object as above, a brick house for example, and try it again and again, varying the length of exposure and the length of development, until you get a negative that prints exactly right. This will teach more in a few mornings than as many weeks of random work. 7. Successes that come by chance are worthless, and prove nothing as to ability. Try to know exactly why you succeed and why you fail. 8. You may often succeed in getting the right exposure the first time, but you cannot be sure of it; yet a careful examination of the first trial ought to enable you to make sure of the second. 9. If the camera needs to be placed in the sunshine, throw the focussing cloth over it before the shutter is drawn out to make the exposure. The direct light of the sun may find its way through rents too small to admit diffused. 10. Once in a while wipe out the camera with a damp cloth to remove dust, which by settling on the plate may cause pin-holes or comets. 11. Treat the lenses with the utmost care. Never leave them about; never wipe them with anything but the softest old linen cambric, perfectly clean, or still better with soft chamois leather, and not even so except when needed. 12. Do not unscrew the tubes unnecessarily to wipe the inside surfaces of the lenses, or for any other purpose, and always do this in dry weather, or you will let in damp air, which will be apt later to leave a dew on the lenses. If any of the lenses are set loosely in the tube, be sure they are replaced with the same side front as before. 13. Do not let either the lenses or the camera stand in the sun, or you may expect warping and splitting of the wood, and discoloration of the lens. 14. Be sure that the camera stand is free from vibration. Uncover the lens very gently so as not to shake the camera in the least, or the definition will be impaired. 15. Unless the ground glass is of the best you cannot focus with 44 A FEW GENERAL RULES FOR BEGINNERS. accuracy. Much of the ground glass in the cameras made for sale is very poor. The glass should, in fact, not be ground at all, but only "grayed," that is, have its surface removed by rubbing with fine emery powder. Focus a brick house 200 feet off with a short focus lens, and if you cannot see the white lines of the mortar either with the naked eye or with a magnifier, the glass is too coarsely ground; and it is to be expected that all the work done with it will be inferior. 16. Focussing with a microscope is less trying to the eyes, and gives sharper work. The larger the lens of the microscope used, the less the eye is strained. An engraver's glass set in horn is good, but a similar one, an inch and a half or two inches in diameter, tires the eyes still less. 17. Learn exactly how to make a negative bath, and then avoid doctoring. For the most part you will only injure it. Add a very little carbonate of soda, and sun it, if out of order, for some hours in direct sunlight, then filter and acidulate as directed for a new bath. Filter first, then acidulate. 18. Decaying organic matter, foul smells, sulphuretted hydrogen, and fumes of ammonia may be expected to produce fog. 19. Do not think it necessary to have the dark room too dark. There may be light enough to work with perfect comfort, and the strain on the eyes in going backwards and forwards will be so much the less: an important consideration. 20. Have nothing to do with cyanide of potassium. It is a sub stance of which the photographer has no real need. If used at all, it should be left to those who have learned their experience on less dangerous materials. 21. Remember that most chemicals are poisons, and that if the fingers are not washed immediately after beintg plunged in them, or if, even with this precaution, they are kept long in the solu tions, mischief may ensue. What this mischief may be is of so gradual and insidious a nature, as to be ascribed to any other cause than the right one. 22. Remnember also that most fumes are injurious. Vapors of ammonia disorganize and paralyze the blood corpuscles. Vapor of ether is very injurious to the nervous system, and depresses the whole tone of the body. Nitric acid is highly poisonous; its fumes, when inhaled, in even a moderately strong form, may cause death in a few hours. 45 INTRODUCTION TO PHOTOGRAPHY. 23. Therefore make every provision for thorough and complete ventilation. And do not fancy (as many most unwisely do) that because your senses become habituated to such fumes, and cease to be inconvenienced by them, that the system is therefore not suffering. 24. Adopt invariably the maxim, that whatever is worth doing is worth doing well. Practice never makes perfect without care, and thoughtful and intelligent observation. Some will do a thing all their lives, and always badly. 25. Acquire the habit of rinsing out all the vessels as soon as emptied, and of not leaving the adhering portion to dry on the bottom and sides, when it will take five times the trouble to get it out. 26. Make it a rule to wash every vessel before you put it away, and again before you use it. Never trust to anything being clean, but make it so. If there is any one thing that is essential in photography, it is care of this sort. The delicate reactions on which photographic processes depend are sufficiently exacting, without further embarrassing the processes by introducing foreign matter of unknown nature. 27. Never forget that no vessel is rendered clean (even if what it has contained has been merely an aqueous solution) by simply pouring water in and throwing it out. Hold therefore the vessel, whether beaker, bowl, bottle, or whatever it may be, under the tap, so that the water may run over every part, inside and out. Outside, because you can never be certain that a glass vessel is clean inside unless you have also made it so outside. Remember that if you hastily rinse out a vessel, you may leave drops of the old solution adhering to the sides above where you have washed, and that a single drop so left may spoil the following operation. This direction may be thought so much a matter of course as to be superfluous, but it is not so. In all cases, except where the old contents are very easily removable by water, employ the bichromate cleaning solution, which for this purpose may be made of double or treble strength, so as to work more energetically. 28. Finally, the beginner in Landscape Photography is earnestly recommended to act upon a definite system. For example, let 46 A FEW GENERAL RULES FOR BEGINNERS. him not run from one lens to another, but rather, having provided himself with one thoroughly good one, let him study out its capabilities and learn exactly how to use it. Different lenses work so differently, that, to the beginner, they are very confusing, and tend to conceal from him the sources of the mistakes and faults that he must necessarily make. Only in one way can he usefully employ himself with several lenses, and that is by using them in succession to take the same view, and observing and studying closely the differences in the results. It has justly been observed by Mr. H. P. Robinson that there is no more effective way of learning than by selecting some one particular view, and working at it till a thoroughly good picture is obtained, regardless as to how numerous the attempts may need to be. One such piece of negative-making, worked thoroughly out, will teach as much as thrice the time spent in random viewtaking. The student should bear steadily in mind that whilst a thoroughly good negative is very valuable, there is nothing mooe worthless than a tolerable one. A tolerable negative is not worth the trouble of printing, and is consequently worth nothing at all. 47 PART II. PHTOTOGRAPHIC OPTICS AND TIHEOPRY OF PERSPECTIVE. A BRIEF exposition of those portions of elementary optics which are of special interest to the photographer seems indispensable to a manual like this; at the same time that it is evident that that only which is essential can be treated of. The subject will be divided into two heads-General, and Special Optics: to which will be added some remarks upon Perspective. CHAPTER I. GENERAL OPTICS. g1.-Reflection and Refraotion. WToEs a ray of light (this expression will be more convenient, although wave of light would be more correct) falls upon any surface, a part is reflected and a part transmitted. Let the ray A 0 (Fig. 4) pass. from the rarer medium on one side of E into the'denser on the other; for example, out of air into glass. Part of the ray will be reflected and a part refracted. In order to study these phenomena, we draw a line perpendicu lar to the surface EBF at the Fig. 4, point of incidence 0. This is the normal, and the angle A 0 N between the incident ray and the normal is the angle of incidence. - -"7.''..., We find that the reflected ray mnakes the angle of }-eflection B 0 A equal to the angle of incidence A ON The refracted ray is bent out of its course towards the normal. In place of continuing on in the direction 0 1, it is deflected towards O N', in the direction 0 R, and the quantity of deflection depends upon the character of the substance. The greater the deflection, the higher the refractive power is said to be. In the foregoing we have considered the case of a ray passing from a rarer medium into a denser. In the converse case the converse result takes place. If in the above figure we suppose the directions to be reversed, and that the ray RO passes at 0 from the denser medium into the rarer above it, then the ray R 0 will be bent away from the normal to precisely the same extent, and will follow the path 0 A. It therefore follows from this that when a ray passes from a rarer medium into a denser, and then through the denser again into the rarer, it will emerge in a direction parallel to that in which it entered, provided that the denser medium has parallel sides. The ray A D (Fig. 5), in passing through the denser medium, takes the course DB, being deflected towards the norma], and, on emerging, again assumes a direction B CUparallel to A D. Fig. 6. A \ _' C T A R But if the sides of the denser medium are not parallel, the ray will not emerge from the second surface parallel to the first direction. Thus the sides 0 E, B F of the denser medium not being parallel, the ray A 0, in passing through the surface B, takes the direction B U. (Fig. 6.) Different substances refract the rays of light very differently, and are therefore said to differ in refractive power. We have a very convenient method of measuring refractive power, which is as follows: In Fig. 7 let S' S" be the boundary line between an upper and rarer substance and a lower and denser one., Let any ray of 4 49 REFRACTION. Fig. 5. GENERAL OPTICS. light R 0 pass at 0 out of the rarer into the denser, and let the line 0 RI' represent its deflected direction. With any distance 0 A as a radius, draw the curve A N' R'. D)raw at the point 0 the,normal SVTN', and from the intersection A let drop the perpendicular A 5, similarly from R' the perpendicular R' S. A S will be the sine of the angle of incidence and R' S the sine of the angle of refraction. Each of these angles will be conveniently measured by its sine. Now it is found that with any two given substances as the rarer and denser medium, the proportion between the lengths of A S and R' S is invariable. If the upper medium be air and the lower a certain quality of glass, the sine of refraction R' S will always be exactly -23 the sine of incidence A S, let the ray fall upon the dividing line S' S" at what angle it may. The ratio of the sines is then invariable for any given substance, and this ratio is called the index of refraction. In the case just mentioned A S being to R' S always as 3 to 2, the index of refraction of such glass is said to be 3 or 1.5. The construction of an angle of refraction is easily made as follows: Let the ray R 0 pass out of air (or rather out of a vacuum, but the difference is unimportant here) into glass of refractive power 1.5. Draw the normal N~' through the point of incidence and perpendicular to the surface. Set off any distance 0 S', and taking this as unity make 0 5" equal to the index of refraction. In this case 0 5' will stand to 0 S' in the proportion of 1.5 to 1. Draw the perpendiculars S' R', S" A. Putting one leg of a compass at 0 and the other at A (the intersection of S" A with 0 R) draw the curve A R', the intersection of this curve with S' R' when connected with 0 gives the path of the refracted ray. ~ 2.-Dispersion. In the foregoing section we have reasoned as if light were homogeneous. But white light is made up of rays of very different 50 Fig. 7. N A ,S' I DISPERSIO!N. refrangibility, so that when a ray of white light A D (fig. S) passes at D) into the denser medium bounded by the line B C, these Fig. 8. D ~ rays are differently affected. The more refrangible rays are bent more out of their course, following the direction D F; the less take the direction D E. On reaching the second surface B D, if this surface is not par. allel to the first, but is inclined to it, these different rays will have their divergence greatly increased, and will be spread out as there represented. We find that a difference of color accompanies a difference of re. frangibility, the most refrangible being violet, and so proceeding in the order, violet, indigo, blue, green, yellow, orange, and red. Under very favorable circumstances, and with well-exercised eyes, a commencing disposition to repeat this gamut, like octaves in musical sounds, is observable, for beyond the red a crimson tint has been seen, and beyond the violet, a lavender. But, independently of these, the existence of nonl-luminous influences beyond the limits of the visible spectrum is easily detected. Beyond the red rays, rays of dark heat are made evident by the thermometer, and beyond the violet there exist rays also invisible, but having a powerful chemical and actinic effect, so that in a portion of space completely dark, sensitive paper is rapidly impressed. Whilst rays, invisible to our eyes, are thus capable of exerting powerful actinic action, other rays, plainly and even brilliantly visible, exercise little or no actinic influence. The yellow and red rays, in which the chief illuminating power of light resides, scarcely act upon sensitive substances. The green rays exert an influence on some and not on others. It is not a little remarkable that sulphate of quinine possesses 51 GENERAL OPTICS. the power of lowering the refrangibility of the rays beyond the violet, and thus rendering them visible to our eyes. If sulphate of quinine be dissolved in water acidulated by sulphuric acid, and the solution be placed in the dark rays beyond the violet, these become visibly blue. CIIAPTER II. OF LENSES. ~ 1.-Nature of Lenses. A LENS may be plane on one side and convex on the otherplano-convex. (Fig. 9.) Plane on one side and concave on the other-plano-concave. (Fig. 10.) Convex on both sides-double convex. (Fig. 11.) Concave on both sides-double concave. Figs. 9. 10. 11. 12. 13. 14. (Fig. 12.) Concave on one side and convex on the other-meniscus. The meniscus may be of two sorts. If the radius of the convex side is the shorter, the lens is thickest in the middle, and is called a positive meniscus. (Fig. 13.) If the concave curve has the shorter radius, the meniscus is thickest at the edges, and is termed a negative meniscus. (Fig. 14.) To understand the action of a lens on rays of light, let us select a plano-convex lens and con Fig. 15. sider its properties. When a ray of light L A falls - t4 Vc' ~from the lens. Now if the centre of /the arrow C has focus at', its ex tremities will have their focus not 60 PI 11 FAULTS INCIDENT TO SPHIERICAL LENSES. in a plane perpendicular to the axis of the lens, but at points nearer to the lens. The whole image, therefore, will not fall upon a plane, but upon a concave surface. As it is necessary that it should be rendered flat, we shall consider the means of doing this by the conjoint operation of the diaphragm and the correc tion of the lens. -)iaphragms.-If a diaphragm or stop were placed immediately in contact with a lens, it would virtually reduce the lens to one the size of the diaphragm. But the diaphragm is always placed some distance away, and then every part of the lens concurs in forming the picture, but each part is only permitted to act upon those rays for which it is intended. Fig. 28. / .1 \, - By the interposition of the diaphragm, the dotted oblique ray, for example, which would reach its focus at a much nearer point, is cut off, and only those rays are permitted to pass which meet at a focus as nearly as possible in the plane in which the central rays find their focus at F. Here is at once a valuable approximation towards a plane field. Moreover, by virtue of the stop the rays which form the image meet with a very small angle, and it is evident that the focussing screen may be brought into such a position that all parts of the image will be very good focus at the same time. This is fiattening the field by use of the diaphraym. Correction.-But the field may also be flattened in the same manner that the correction for chromatic aberration is applied. 61 GENERAL OPTICS. Fig. 29. In the simple lens, as seen in Fig. 29, the field is very curved. If we now add the correcting negative lens to remove the color, we shall lengthen out the oblique pencils more than the central, as seen in Fig. 30. This is flattening the field by correction of the lens. Fig. 30.' As this correction may be applied to any extent, it nmav even be carried so far as to bend the field backward, and throw the foci of the o)blique pencils beyond the plane of the central ones. g 5.-Distortion. The mathematical conception of a lens regards it as consisting merely of its bounding planes, and destitute of thickness. If lenses actually possessed this form, the images produced by them would correspond strictly with the principles already laid down. But all lenses necessarily possessing a definite thickness, the image is thereby deformed, unless special measures be taken to correct such distortion. Every right line, no matter what be its inclination, if it be directly in front of be lens, so that the prolongation of the axis of the lens passes through it, is imaged on the screen as a right line, whether perpendicular, horizontal, or inclined, because of its symmetrical position with respect to the different parts of the lens. But if the line be not symmetrically placed, that is, if the prolong,ation of the axis of the lens do not pass through it, then the By an error of the engraver the oblique rays of this figure have not been deflected at the lens. 62 FOCAL LENGTHS OF LENSES. image of such a right line will be curved, with its concavity turned toward the axis of the lens, and a square, for example, will be represented, as in Fig. 31. Fig. 31. This is termed barrel distortion, and is seen in the single view lens. The position of the diap)hragm has necessarily a strong influence on distortion. When the diaphragm is in front of the lens, as in the case of the view lens, the crossing of the rays takes place in front of the lens, and the lower part of the lens receives the rays from the upper part of the object, and the distortion is barrel-shaped. If the diaphragm be placed behind the lens, the crossing of the rays takes place behind the lens, and the lower part of the lens receives the rays from the lower part of the object. If now we take the case of two lenses with a stop between, as in photographic doublets, the one compensates the other, and the distortion disappears completely if the lenses be exactly similar and the stop be placed equidistant from each. CHAPTER IV. FOCAL LENGTHIIS OF LENSES. ~ t.-Images of External Objects. NOTHING iS more important to the photographer than to have a clear conception of the action of lenses in forming images of objects; and this the writer will endeavor to present in a manner as simple and as much divested of technicalities as possible. If in the shutter of a dark room we make a small opening, images of external objects will be formed upon the opposite wall; and it is important to the student to remark that these images are formed without the interposition of any lens whatever. If several small openings be made at irregular distances, several images of the whole external view will be formed upon the wall, irregularly superposed upon one another, and consequently producing complete confusion. If, now, these various openings be supposed to approach each other until they join, they will 63 I. GENERAL OPTICS. form one larger opening. The confusion spoken of before will now be materially diminished. Although each part of the opetring produces its separate image, yet all these innumerable images will be more or less nearly superposed. External objects will be recognizable, but their borders will be indistinct and undefined. The brihtness of the picture will increase exactly with the area of the opening, and diminish as it diminishes. We thus find ourselves in the dilemma, that to obtain a welldefined image, the opening must be so diminished' that the illumination becomes utterly insufficient. On the other hand, where the opening is large enough to give a good illumination, the definition is totally destroyed. It is here that the lens gives us its indispensable aid; and the manner in which this aid is given is exceedingly instructive. Let A be the opening in a shutter, Fig. 32. the image D) E of any external ob 8i\~~~ ~ject, B C will be formed on the wall behind the opening. _~~But the image of each point in the external object will be expanded D over a considerable surface, and will c ~h\> I C, C. Double convex crown glass lenses. F, F. Double concave flint. C'. Double concave crown. P'. Double convex flint. D. Diaphragm with its opening at F.', f, f. Flange. edly, but since critically examining its power, the writer finds himself led to the following comparison: For architectural objects, it is surpassed by Zentmayer's lens, which gives lines equally straight, and includes a very much larger angle. Where angle is no object, where we have free open space to the desired direction about the architectural object, there only the triplet has an advantage in the larger diaphragm and quicker actions which it admits of. For copying, it is surpassed by the same lens. For views not embracing architectural objects, or where these are not near the margin, and are inconspicuous, it is undoubtedly surpassed by the view lens, especially by Dallmeyer's wide angle view lens. For portraiture, it is inferior to the portrait lens, being much slower. By removing the central negative lens, however, its 78 I PHOTOGRAPHIC OBJECTIVES. action is increased; but the centre of the image only is sharp enough for use, as in the case of portraits to be vignetted. For groups it is the best lens that we have, unless it shall prove to be surpassed by Steinheil's new Aplanatic, and Dallmeyer's Rapid Rectilinear, as now seems possible. The triplet may, therefore, be considered as a servant of all work, but (except in the case of groups) scarcely doing any of it as well as lens especially made for that specific work. For such amateurs as wish to do a variety of work, but feel that they can allow themselves but one lens, it will be an appropriate acquisition. It should be distinctly understood that a good triplet is capable of doing almost any photographic work well, that it is, in fact, the only approach we have to a universal lens. Some beautiful landscapes, by G. W. Wilson and other distinguished photographers, have been taken with it, and exquisite copying work. Perhaps my meaning will be more clear, if I say that some landscapes can be taken fully as artistically with the triplet as with the view lens, but others again cannot. Some engravings can be copied very well by the triplet, but in other cases of copying, particularly where extreme exactness is needed, it is surpassed by other lenses. The triplet possesses one advantage, which must not be passed over. An extension of the size of the diaphragm, whilst it greatly impairs marginal definition, does not at the same time destroy that of the centre. Consequently, where rapid work is wanted, as in taking photographs of animals, instantaneous views, &c., it may advantageously be employed. Of course, the size of the plate to be covered must be proportionately diminished, or else want of definition at the margin must be submitted to. It is evident, however, that if we can cover a half plate by using a whole plate lens with large diaphragm, and so greatly shorten the exposure, we have what, in many cases, is a very ma terial advantage. And this we gain with the triplet. The many surfaces of glass in the lenses composing the triplet is an objection to it, as tending to the introduction of diffuse light into the camera. Triplets made by different makers vary very much in their performances, especially in the size of stop with which they will work, and their value is always in proportion to the size of stop with which they can be satisfactorily used. 79 SPECIAL OPTICS. ~ 4.-The Globe Lens. as devised in this country by Mr. tred by him in connection with the lteristic feathre lies in this, that the nt, form part of one and the same placed at the,9ntre of that sphere. the incident ray'R, Fig. 52, which passes through the centre, has a nearly perpendicular incidence upon the outside surface. It there fore undergoes but little deviation at either of the four surfaces, but necessarily encounters some, and is bent from its original direction R P down to D. More erroneous statements, both favorable and unfavorable, have been published in respect of this, than of any other lens that ever was invented. The inven ] C.i n fn1 D F f C, C. Positive menisci of crown glass. F, F. Negative menisci of flint glass. -D. Diaphragm. f,.f. Flange. tors claimed too much for it, whilst some of its critics made unjustifiable misstatements re specting it. Its appearance un questionably made an era in phothe power of the photographer to angle never before possible. This Fig. 52. improvement was so well appreciated, that the lenses were strained'to cover more than they properly could, an effect at 80 tggraphy, by putting it into I. - .obtain pictures embracing an D RI PHOTOGRAPHIC OBJECTIVES. tainable only by using the very small stops. It resulted that flat and meaningless pictures were produced in great quantities, and the advance of landscape photography in America was materially retarded, for these lenses acquired a great popularity here, and for a time nearly superseded all others for landscape work. Great numbers were also exported. The form of lens was also largely imitated abroad, both by exact reproductions and by modified forms, depending upon the same idea. This and another American lens, that of Mr. Zentmayer, are remarkable for the absolutely true perspective which they give. Where a great breadth of what is known to artists as "parallel perspective" is represented, the triplet gives a slight convergence, as the writer has convinced himself by actual measurement, whereas the globe preserves a perfect parallelism. It is to be concluded, therefore, that when the globe is judiciously employed-that is, when the smallest stop, and, if practicable, the next to smallest is avoided, and it is not sought to cover too large a plate-it is capable of doing good work. It is in one respect like the triplet, that is, it is capable of being turned to a great variety of uses-landscape work, portraiture, architectural reproductions, and copying, in each of which-certainly at least in the first two, and probably in the others-it is surpassed by other lenses. ~ 5.-The Zentmayer Lens. Mr. Joseph Zentmayer, of this city, photographic objective of a single sort of glass, his lenses being both uncorrected menisci. Nevertheless, in these objectives the chemical and visual foci are practically coincident. Tlhis single fact would be enough to invest the lens with interest, but its performances are sufficiently remarkable to indicate that this lens will be adopted for all those descriptions of work to which it is especially suited. Fig. 53 will give a clear idea of the system of construction. The front and back curves of each lens 6 81 has succeeded in making a Fig. 53. D i I I D. Diaphragm. f, f. Flange. " SPECIAL O.PTICS. stand to each other in the relation of 12 to 13, and the two lenses to each other in the ratio of 2 to 3. The stop is advanced a little nearer to the front lens than the centre of curvature.of the exterior surface of the larger lens. It is evident that by having a series of lenses of different sizes, the larger lens of one pair may serve as the smaller lens for the next larger pair. On this principle these lenses are manufactured. The complete sets embrace six lenses, capable of forming five pairs, having a great range of focal lengths. Smaller sets are made, in which four lenses form three pairs. The revolving diaphragms are furnished with three holes. The larger of these is simply for focussing, and cannot be used for photography, the image so attained,being quite destitute of definition. The middle stop is the most generally useful. These lenses include a wonderful angle- fully as much as can ever be advantageously used, and much more than covered by the globe lens. The architectural effects attained are good, and bolder than would be expected from the small size of the stop that must be used. The reflecting surfaces which the ray meets in this lens are fewer than in any other centrally stopped objective, and this gives brilliancy as well as diminishes the proportion of light lost. For copying these lenses are at least as good as any, and perhaps better. As they are not achromatized, the cost of making is greatly diminished. It is affirmed that these lenses give a circular field of very nearly double their focal length, and this computed by their true focal length, which, of course, is longer than the "back focus" often used to roughly indicate the focal length of lenses. In comparing different lenses, it is always necessary to bear this carefully in mind, otherwise injustice is done. The focal lengths by.which Zentmayer's lenses are known, are always the true focal lengths. Those advertised to the globe lenses are the "back foci," than which the true focal lengths may be one-half longer, as, for example, a globe lens in my possession sold as a "3-inch," has, in fact, a focal length of 4-2 inches when correctly measured.' Public opinion should compel all opticians to sell their lenses under the designations of their true, absolute, or " equivalent" foci. No other system does justice to the purchaser. 82 PHIOTOGRAPHIC OBJECTIVES. ~ 6.-The Steinheil Lens. The lerns of Professor Steinheil, like the foregoing, consists of a pair of uncorrected menisci, but in this case of equal size. The visual and chemical foci do not here coincide, but require a correction. The focussing screen, after taking the usual focus, must be returned s41 for very distant objects, and materially more for near ones. For exam- Fig.54. ple, if the object and the image be of equal size, the correction will be about'2, and in- termediate for intermediate distances. The inconvenience of this correction is a sufficient objection to the lens. It gives, however, a very remarkable angle; and it is \ wonderful to see how large a picture is produced by a very small lens of this description. As the diaphragm is small, the illumination is consequently faint, and the exposure prolonged. This lens is not the less a remarkable optical work, though less so than Zentmayer's, with which its discovery appears to have taken place at nearly the same time. Both forms are patented. Steinheil has lately constructed an achromatized doublet, to which he gives the name of "aplanatic," which has proved itself to be a useful lens. Like the triplet and globe, it may be employed for taking groups, portraits, and views. Its sphere of utility corresponds nearly with that of a good triplet, whilst it includes a much larger angle. In using it the focus must invariably be taken with the largest stop, and then a smaller must be introduced to give the necessary sharpness. This evidently creates a difficulty in deciding how small a stop is needed in any particular case. Nevertheless, the instrument has been very highly spoken of by good judges. ~ 7.-Ross's Doublet. Mr. Ross's form of doublet, Fig. 55, has been favorably spoken of. It is intended for views and architecture, of which last it preserves the straight lines, and for copying. A material convenience is afforded with this lens, an internal shutter, sliding across the opening of the diaphragm, instead of covering and un 83 SPECIAL OPTICS. covering the lens in the usual way with a cap. This feature has been also introduced into Zentmayer's lenses. Ross's lenses may be separated, and each can be used as a single landscape lens. L, L. Positive menisci, corrected. D. Diaphragm. f, f. Flange. ~ 8.-Other Forms of Photographic Lenses. Orthoscopic Lens.-This form which, like the portrait lens, we owe to Petzval, has been extensively used, especially in this country. Harrison manufactured many good objectives of this form; but on introducing the globe lens, he stopped making the'orthoscopic, and this lens is now but little used here. In Germany it seems to have kept its place better. The orthoscopic is a good copying lens, but slow, owing to its long focus, and the small stop generally used with it in copying. For taking views, a stop of considerable size may be employed; and, as it has a considerable depth of focus, it is by some much prized for landscape work; though this is rather in Germany than here. Small pictures of landscape scenery are well taken by the smaller orthoscopic lenses, because in them the focal length is not far from corresponding with that of the eye. But large pictures made with the orthoscopic require a lens of very long focus; and it results that planes of distance are not well rendered, the foregrounds become indistinct and inconspicuous, and distant objects look unnaturally near. Busch's Pantascope consists of two corrected lenses with a central stop. It includes a very large angle of view, and has been highly spoken of. A very carefully constructed camera appears to be necessary for it. Rectilinear, and Rapid Rectilinear.-Dallmeyer has lately introduced two new lenses under these two names, which, though similar enough to lead possibly to confusion, characterize very different lenses. The Rectilinear was introduced in 1867. A 84 Fig. 55. PHOTOGRAPHIC OBJECTIVES. specimen examined by the writer was a good deal similar to the globe, but a better lens, including a wider angle, and apparently free from "ghost" or flare. The Rapid Rectilinear the writer has not seen. It is described as made of flint corrected by flint, in this resembling Steinheil's aplanatic, in which respect Dallmeyer claims precedence of Steinheil. It has just been introduced, and will probably prove a valuable instrument. The first includes an angle of 100~, the latter of about 60~, but is more rapid. The Fitz Lens.-The late Mr. Fitz, of New York, just before his death, had completed a form of lens, which, however, does not seem to have been able to compete successfully with the other new lenses introduced about the same time. The Ratio Lens was introduced a short time back by Mr. Harrison's successors. It consists of a pair of achromatized lenses of different sizes, and adapted so that the larger lens of one pair may become the smaller lens of a larger pair, in the same way as described in Zentmayer's. Panoramic Cameras.-The theory of this very ingenious instrument, by which such beautiful results have been obtained, is as follows: Let J be the centre of emission of the cone of rays coming out from any objective, single, double, Fig. 56. or triple, which finds its focus on the screen S S'. If now the lens be made to ro-.4 tate horizontally, on J as a centre, the position of objects in the image r formed on the focussing screen will not change. If the image of any exterior object, for example, falls at the centre F, the rotation of the s lens will not cause the image of that body to move, but it will remain accurately at F until the lens rotates so much that it passes out of the field of view. Now, to avail ourselves of this property, we must remember that when the lens is rotated so that its axis passes from the direction J A to the direction J A', its image is no longer in focus on the screen at A', but at the point F; because the central ray is now in the direction JA', and its focal length will be the same it originally was, viz., J,Por J F'. 85 SPECIAL OPTICS. The first idea for applying these principles would evidently be to use a sensitive plate of a cylindrical form, corresponding with the curve F" F F', and by means of a mask with a vertical slit, to conceal all the plate but a high narrow strip at the centre; then if the plate F" F F' remained stationary, and the lens rotated carrying the mask with it, every part of the plate would be exposed successively. But in the instrument now in use, this is otherwise managed. The sensitive plate occupies the position S S', and is flat. It is masked, with a narrow opening at F, extending from top to bottom. As the lens rotates, the plate SS' is shifted sideways by a system of clockwork, which makes its movement exactly cor respond with that of the lens, whether it be slow or fast, as the light may require. As a curved plate, F' F F" would receive a perfect image from the rotating lens, masked as above explained, all that is necessary is, that the flat plate S S' should be shifted in such a way that when, for instance, the lens has moved so that its axis is in the direction J F', then the plate shall have been brought up to F', there to receive its image at its correct focus. And, evidently, if the plate be long enough, and the camera be rotated to a full circle, an entire panorama may be obtained. This picture will be found to differ materially from one obtained in the ordinary camera. It will be in panoramic, instead of plane projection. The picture will not be an harmonious whole, which the eye sees whilst regarding its perspective centre, but as if the eye were directed always at the object opposite to it, in whatever direction it chanced to look, or, to speak more exactly, as if the eyes were directed in succession at all the vertical lines in the picture. Another difference will be that from end to end (but not from top to bottom) the picture, no matter how large, will be in equally good focus. At the right and left extremities the picture will be as sharp as the middle. This is because the central part of the image'only is used. Each part becomes'successively the centre. Again, the vertical slit at F may be made narrow at bottom and wide at top, so that the foreground will get a larger exposure than the sky; and this difference may be regulated at will, giving, if desired, to the sky an exposure of one-tenth or less than that which the foreground receives It is this which has enabled 86 PHOTOGRAPHIC OBJECTIVES. Braun to produce such wonderful cloud pictures in his Swiss scenery, and to get good definition of snow mountains against the sky and clouds. The most successful application of this principle is at present Johnson's panoramic camera. It is patented, but the patent cannot cover the principle, which was understood many years before his application of it, and was applied to the construction of panoramic cameras.1 ~ 9.-General Remarks on Lenses. In the foregoing sections all the forms of lenses possessing any interest to the photographer have been described. It remains to say a few words on the use of them. Portraiture.-The portrait lens is so far superior to all others for this purpose that none other is habitually used. When the light is strong, a tolerable portrait can be got with a triplet or Steinheil aplanatic or a globe; generally it is necessary to work out of doors to obtain a sufficient illumination, and avoid a very protracted exposure. For card portraits the focal length needed for the lens will depend upon how mufch is to be included. For full lengths, very short focus lenses are commonly employed. For such as show part of the body, and even including the hands, lenses of six to eight inches focal length will be proper. For "cabinet size" lenses of eight to ten inches focal length will be needed. For 6-1 x 821 plates and half length portraits, a ten inch focus lens will be suitable. For very short exposures, especially inl taking children, "extra rapid" lenses are made, with very short focal lengths. Some makers make a difference in their lenses according as they are wanted for full lengths and for vignetted heads. In the latter case every effort is made for perfect definition at the centre; in the former a good definition all over the plate is aimed at. Generally, the shorter the focal length, the less exposure will be needed; but the longer the focal length, the less exaggeration there will be in those parts that project, the hands especially. Very ingenious arrangements have been adapted to the portrait I See Secretan, De la distanc e focale des Systemnes Optijues convergents. Paris, 1855. 87 SPECIAL OPTICS. lens, with the object of changing the focus during exposure, in the effort to get a diffusion of focus, and, instead of having one part sharp to the exclusion of the rest, to maintain a certain average of sharpness over the whole. Even lenses have been made in which a certain amount of spherical aberration has been left uncorrected, in order to diffuse the sharpness. The late Mr. Clandet brought this whole subject prominently forward shortly before his death, and opinions are very much divided on the subject. Flare or ghost in the camera is an image of the diaphragm. Let C be the centre of curvature of the second surface of the lens, Fig. 57. whose thickness is here intentionally exaggerated, in order to make the lines visibly distinct. A ray R, passing through the diaphragm, strikes the first surface, is refracted, and passes to the second. Here it is divided-most passing onwards in a direction R' to form the true image, but a part suffering reflection and returning to the first surface. Here most is transmitted, but a part is reflected again and returns to the second surface. The greater part is transmitted, and undergoing refraction is bent down to the axis at some point F', producing the flare. Comparing Lenses.-A great deal of unintentional injustice is done by photographers in comparing lenses for want of taking the necessary precautions to make the test a just one. It should invariably be borne in mind that the performance of a lens depends entirely upon its stopping down. Of two lenses compared, the inferior one may easily be made to seem the best, if it be used with a smaller stop, and no account be taken of the time of exposure. It may be taken for granted that the sharpness, depth of focus, and size of good picture obtained will always increase as the size of the stop is diminished. This has led many landscapists to the use of extremely small stops habitually, esteeming it of little 88 L F' R PHOTOGRAPHIC OBJECTIVES. consequence to wait longer for the impression to be made. Several evils result therefrom. 1. It may be taken as an invariable rule that the larger the stop used, the more detail to the shadows will be obtained, always supposing that each trial has been made with a correctly timed exposure. Let us say that, with a half inch stop, fifteen seconds have been found exactly right. Now, using a quarter inch stop, we must, of course, expose for one minute.' The exposure will be correct; the picture will be the best obtainable with that size of stop, but the detail to the shadows will not be so good as in the former case. 2. It seems well established that a large stop always gives a bolder picture. A small stop, especially if less than one-thirtieth the focal length, leads to flatness. 3. A long exposure in the case of portraiture is a serious evil. Even with landscapes it is not unimportant, for, although the contrary has been affirmed, the difficulty of catching foliage still always increases with the length of the exposure. But in comparing lenses of different focal lengths, the absolute size of the stop is not the criterion, but the relative. For example, let it be required to compare the performance of a triplet of twelve inches focal length with a single view lens of six, the focal lengths being in both cases the absolute or equivalent, not the "back focus." A proper average stop for a twelve-inch lens is half an inch; the stop is then one twenity-fourth the focal length, which may be conveniently expressed f24. The single lens, then, must also be tried with an f24 stop, in its case evidently one-quarter inch. Having taken with great care the best focus for each lens, let negatives be taken. First, compare the definition at the centre. Some writers hold that the central definition of a good triplet exceeds that of the best single lenses. Others, equally reliable, maintain the opposite opinion. Having settled that point for the particular case, pass from the centre towards the margin. What falling off the 6-inch lens shows at 2 inches from the centre, the 12-inch must not show 'The exposure must always be inversely proportioned to the area of the stop, and this area is proportional to the square of the diameter of the stop. 89 GENERAL OPTICS. till 4. And to compare the marginal definition, the 12-inch lens must have its print cut 4 times as large. If it be tested on a 6( x 821 plate, the 6-inch lens must only be compared with a field of 3I x 4.1 As for definition, so also for depth of focus. It must be exa mined under the same guarded conditions. To try two lenses together, with stops not corresponding to their focal lengths, is to obtain utterly unreliable results, and yet this is constantly done. Take any common lens, cover its diaphragm with a piece of opaque yellow paper, and make a pinhole in it, not too small. There will at once be wonderful sharpness, and near and distant objects will be all in perfect focus at once. The principle of cutting off all the rays that do not meet the axis has been carried to great length, and the result is remarkable depth of focus and definition. But a negative so taken is worthless. The effect is fiat, the exposure excessively prolonged, and contrasts too great. To compare portrait lenses proceed as follows: Measure the focal length of the lens habitually used, and which is to be the standard of comparison, and that of the new one. As both are of the same construction, it will be sufficient to measure from the diaphragm to the ground glass. Measure with a pair of com passes the diaphragm you habitually use, and then set the new lens to the corresponding diaphragm in proportion to its focal length. If the one has, for example, a focal length 4 longer than the other, let its diaphragm be ~ more in diameter, and so on. Hlaving repeated this, give the new lens the same exposure, with the same light, as the old, and a comparison of the results under these conditions will show which is the quicker, which gives the better definition, depth of focus, &c. It is necessary, however, in all cases, to remember that even with proportionate diaphragms, lenses of different focal length cannot be accurately compared, as the proportion of performance always falls off as the focal length increases. Selection of Lenses.-Much that has just been said't the comparison of lenses will necessarily control their selection; but * some additional points need to be adverted to. The color of a lens is always important. Place the lens on a perfectly white sheet of paper-any brownness of tint is a serious objection. In an old lens this may arise from the Canada balsam, with which the separate portions are cemented together, 90 PHOTOGRAPHIC OBJECTIVES. turning yellow. If this be thought to be the case, the lens should be taken to an optician to be separated, cleaned, and re-attached. The photographer is not advised to attempt this himself. Bubbles in the glass are objectionable, because they tend to throw rays in abnormal directions, and to impair the brilliancy of the image. One or two small ones are not important, nor a sufficient cause for rejecting an otherwise satisfactory lens. But it indicates carelessness in the maker, as these bubbles are always visible in the disk from which the lens is made, and such disks should be rejected. Strin, hair-like or thready transparent lines, are very objectionable, and at once a sufficient cause for rejection. Scratches.-Lenses will sometimes come from the maker with scratches, the result of careless handling of tools in setting, or of bad packing. Such of course are returned. Centering.-To every lens there belongs an optical axis, a line perpendicular to the surface of the lens, and passing through its centre of curvature. Every achromatized lens consists of at least two portions, and it is necessary that these should be so arranged when attached together by the balsam used for that purpose, that the optical axis of each should exactly correspond. When two lenses or more are united to form an objective, not only must the parts of each be properly disposed, but the front lens must have its axis coincident with that of the back lens. This will depend upon correct mounting. The usual way in which opticians test the correctness of the centering, is by making the tube containing the lenses revolve in an upright position, that is, with the lenses horizontal. If, now, a candle be placed at a little distance, and the eye be placed at a convenient position, the candle will be seen reflected from the surface as a bright point. Every surface of every piece of glass in the tube will send back a reflection. Next the tube is caused to rotate. Each lens that is correctly centered will continue to send its reflection back perfectly fixed and immovable; but any surface that is out of centre will cause its reflection to deviate more or less according to the amount of error. It is evidently not necessary that all the reflections should be seen at once, but they may be observed succtessively. This method of observing evidently renders it easy to fix which, if any, of the surfaces is erroneously placed, and in which direction is its error. 91 GENERAL OPTICS. Another mode of observation is more convenient for the photographer, as not requiring the apparatus needed by the method just described. The observer places himself in a dark room with a single candle. Standing five or six feet from it, he looks at it through the objective, inclining the latter a little until he sees a series of bright points, which are the images of the candle, produced by successive reflections from the different surfaces of the lens. When a lens has four pieces of glass in its construction, as in the case of the portrait, globe, orthoscopic, and some other lenses, the number of possible images is very considerable. These cannot generally be all found at once, but eight, ten, or more can be counted; a little practice, and altering the inclination of the lens materially aids in increasing the number. If now the centering is perfect, it will be found that, by carefully adjusting the position of the lens, all of these reflections can be made to range themselves in a straight line. But if any one or more of the component parts is out of centre, this will be found impracticable. One or more of the bright points will remain obstinately out of line; and, when a little movement is made which brings them in, it will be found that some other image, previously in line, has slid out of it. When the observer, after very careful trial, finds that it is positively impossible to make all the images range, he will be justified in concluding that there is a fault in the centering. Whilst this test is so easy that any intelligent observer can apply it at once, there is no doubt that it is a very severe one. A lens may perform quite fairly, and yet such an examination as this may reveal a defect. But there is no doubt that first-rate excellence is incompatible with such defectiveness. It is also evident that the fewer the pieces of which a lens is composed,.the less difficulty the optician will find in getting them all in correct line. Quickness.-When lenses are tested with equal stops (in proportion to their focal length), their comparative quickness will depend upon the whiteness of the glass, the fewer number of surfaces that enter into their formation, and on the curves given by the optician: careful testing and this alone can settle the point. Chemical Focus.-The correction for chromatic aberration is now greatly better made than formerly. To test whether a lens is 92 PHOTOGRAPHIC OBJECTIVES. properly corrected, select a newspaper printed with sharp-cut type, and paste a piece a foot or fifteen inches square upon a smooth piece of board. Set this up before the camera, with the columns vertical, but inclined in a slanting direction, so that one side, the right, for example, shall be a couple of inches nearer the camera than the left, keeping the board, however, exactly upright. Focus carefully along the central upright line, and copy it full size, or thereabouts. Next examine the hair-strokes of the letters on the negative with a microscope. If the lens is properly corrected, the central line should be in the sharpest focus. If, however, it be found that a portion to the right or left of the central line is in better focus than the centre, then the correction has evidently been faulty. If the sharpest image is of a part nearer to the lens than the centre, the lens is under-corrected; if of a part further from the centre, the lens is over-corrected. In either case, it is said to have a "chemical focus," that is, its chemical and visual focus does not correspond, a fault of the first magnitude, and sufficient cause for rejecting the lens entirely. ~ 10.-Care of Lenses. A few words on the preservation and care of these beautiful products of science and art will not be inappropriate here. When lenses have been out of use for some time, and have been carried to a distance, they should be carefully unscrewed and wiped out with a piece of soft clean chamois leather. The palmn of an old white kid glove may be used, or a soft old linen handkerchief, but the leather is preferable. Nothing else should be used than the substances here named. If the lenses have stood only for a short time, they may only require wiping on the exterior surfaces. They should first be examined, and if free from dust, it is better not to wipe them. Too much wiping is as bad as too little, and it may be set down as a general principle, that the less lenses are touched with anything the better; especially the fingers should never touch them. With Dallmeyer's wide angle view lenses, convenient caps of morocco lined with velvet are furnished. This is an excellent arrangement, as dust is excluded, and the amount of wiping is diminished. These caps are also very convenient for covering 93 GENERAL OPTICS. and uncovering the lens. Such should be made and furnished with all photographic objectives. Something similar, or a light brass cap, to protect the back lens, would also be very useful with all lenses intended for field use. It is a disadvantage to keep the lens in a cold place, and then, perhaps, suddenly remove it to a warm one. A dew may form on the lens while the image is being impressed, or before, and may escape observation. Lenses should never be left lying where the sun, or even a bright light, can fall upon them, as strong light. has a tendency to darken the color of the glass and increase the exposure necessary. For this reason, where stereoscopic lenses are occasionally used separately, this use should be divided between the two. If one of the pair is always used on such occasions, it will tend gradually to work more slowly than the other, so that the two can no longer be used advantageously together. The care of the lens should also be extended to the brass mounting. If this is allowed to become dented, or is in any way roughly treated, there is danger that the centering may be interfered with, and the working of the objective thereby impaired. Second-hand objectives should always be severely tested before purchasing, and no one should be induced to acquire a lens in this way, unless he feels fully capable of judging the objective on its own merits by a careful trial. CHAPTE'R VI. PHOTOGRAPHIC PERSPECTIVE. ~ 1.-Nature of the Image formed by a Lens. WITH the progress of photographic study there comes a general feeling amongst the more intelligent photographers that their art connects itself'with Art especially so called, and that a knowledge of some of its fundamental principles should accompany the study of photography. Particularly, the photographer should have an elementary idea of Perspective. This must necessarily be gathered from appropriate manuals, for to explain it here, even in a 94 PHOTOGRAPHIC PERSPECTIVE. very elementary fashion, would exceed the limits of this volume. The writer can only with appropriateness undertake to supply here what would be found wanting in any manual of perspective, viz., the application of the laws of perspective to the operations of photography. Whenever a solid object is to be correctly represented upon a flat surface, it must either be laid out according to certain definite rules, as by the draughtsman, or the same thing must be accomplished mechanically, as done by the camera. In either case, the result is the same. The delineation of a solid body, or of a scene, or an edifice, as made by a draughtsman, is, in its essential features, precisely the same as that made by the lens; both, however, are subject to certain rules. If we observe a building through a large pane of glass in a window, and if, our eye remaining stationary, we mark on the pane a series of dots, each exactly corresponding to some corner of the edifice, and then connect these dots, we may thus form a perfect outline of the building, every line of which will perfectly correspond to the same line in the building, covering it, as it were, as we look. This will be one perfect perspective drawing of the building. If, now-still keeping our eye exactly opposite the centre of the pane-we draw back, so as to be farther from the window, the correspondence no longer exists, every line of the building has started out, beyond the corresponding line of the original drawing; and we obtain a larger picture than before. By altering the position of the eye any number of different pictures will be obtained of the same scene, and these correspond with the pictures obtained from lenses whose absolute focal lengths are equal to the distance of the eye from the pane of glass. If the arrow A B, fig 58, represent the edifice, P' P' the pane Fig. 58. 95 P.1 ~~~~~~IB a PHOTOGRAPHIC PERSPECTIVE. of glass, and E the eye, the edifice as represented on the pane will have the height P P. If the eye be withdrawn to E', the image will be enlarged to P' P'. Now, if the eye be replaced by a lens whose focal length is the same as the distance of the eye from the pane, the image formed by that lens will be precisely the same as seen by the eye-reversed, of course. The lens L forms on the screen an image I' (Fig. 59) of the arrow precisely as large as the image I seen by the eye when placed at L, upon the pane at ], the distance of the eye to the pane being the same as the focal length of the lens; that is, the distance from L to the centre of the arrow. 1 ^A T-/T~~~~~~" I~~\ If now, keeping the eye at L, we move the pane, backwards and forwards, we shall obtain any number of images of the object A B. By drawing lines from L to all parts of A B, it will be seen that the triangles are always similar; that is, any triangle E A B (Fig. 58) will always be similar to the corresponding triangle E P P. All parts of the image P P will therefore have the same proportion to the corresponding parts of the object A B. If any one dimension be altered, or if P P be increased to P' p' by drawing back the eye to E', all others will be proportionately changed. It follows, therefore (and this is very important), that all these images of the object will vary in size only; that is, they will be magnified or reduced images of each other; and as these inmages are identical with those formed by lenses placed at L (Fig. 59), having focal lengths respectively equal to any distance from the eye to the pane, we draw the conclusion that similar lenses of different focal lengths, placed at the same spot, give representations which differ from each other in size only. If the picture given by a small lens be magnified (for example, in a solar camera) to the size of the picture given by a large lens, the resulting picture will be identical with it, supposing the lenses to be perfect instruments. The perspective angles will be the same. If A B C D be the side of a house seen obliquely, the top and bottom lines, if continued, will meet at a vanishing point V, and 96 Fig. 59. PERSPECTIVE ANGLES. the perspective angle B VA will Fig. 60. be greater or smaller, according as we place ourselves nearer to,' or farther from the building. The nearer we approach the nearer the point V comes in, and the 4 more abruptly the apparent size diminishes from A B to C D. As any good photographic lens placed in the same position as the eye gives the same result, it follows that the nearer we go with our lens to the edifice, the sharper will be the perspective angle at B. For example, the side of a house, which, when seen in perspective from a little distance, gives the effect A B C D (Fig. 61), changes as we approach, and assumes the appearance A B c b, with the much sharper angle at B. So that the same lens which depicted this house from a distance Fig. 61. with the angles A B C D, will, when brought much nearer, give the effect A B c b. This case is, therefore, to be very clearly distinguished from that which we before considered, and where the eye was simply brought nearer to or further from the plane on which the image was drawn. In the present case we suppose the plane itself to be removed from the building. In the first case the perspective angles did not change; in the second they do. There is a certain subtlety in applying these principles to practice, which requires close attention. Although the character of the image as distinguished from its mere size, depends upon the distance to which we go from the object, and not upon the lens, yet, nevertheless, lenses of small focal lengths give almost always very incorrect pictures, because such lenses are brought too near to the objects, and the sharp perspective angle c B A results, 7 97 B v v 6 4 PHOTOGRAPHIC PERSPECTIVE. which is always offensive, and may legitimately be termed incorrect, because it gives incorrect conceptions of the object delineated. A larger lens should be used, and taken to a greater distance. If, for example, it be required to photograph a large edifice, so that the image shall be only 3 inches high, and we take a 4-inch lens and go to such a distance as will secure the size required, we shall get a picture with the sharp angle c B A; but if we take a lens of 8 to 10 inches focus, and go to such a distance that the image is reduced to the same height, 3 inches, we shall get a natural angle CB A, the actual apparent height A B remaining the same in both cases. The practical application of these rules is further somewhat complicated by the fact that it is necessary to take into consideration the actual size of the picture; for it is an unquestionable fact that the eye will sqtpport perspective angles in a large picture, that it will not in a small one. If, for example, we take any small picture c B A, and magnify it considerably, we shall find that the perspective angles, before entirely too sharp, lose this effect, and seem natural. (The experiment is a surprising one, and must be tried to be appreciated.) This is one reason why the small photographs taken with very short focus lenses are so much improved by magnifying them. Their caricatured perspective, intolerable in such small pictures, becomes endurable in the large one. On the other hand, a large picture, in which the perspective is appropriate and suitable for its size, cannot be reduced without injury. Even if the reduction be absolutely perfect, as when executed by a copying camera, the character of the design is destroyed. Engravers know this, and know that a large architectural drawing cannot be reduced with advantage; and the same truth is recognized by all artists. Ruskin remarks that true perspective is infinite and unreducible in its nature. To every size of representation there is a certain size of perspective angle appropriate, or rather the appropriate size lies within certain limits, and these are only to be fixed by judgment and cultivated taste. Farther, it is to be remarked, that as in every photographic image the focal length of the lens corresponds with the distance of the eye from the section on the window-pane before spoken of, it follows that every photographic picture, to give a correct im 98 PERSPECTIVE ANGLES. pression, should be held from the eye at a distance equal to the focal length of the lens with which it was taken. It will be at once apparent that a view taken with a lens of 4 or 5 inches focus, cannot be held that near to the eye of a person with ordinary sight. It follows, therefore, that such lenses never can give truthful delineations of scenery. They may make pretty pictures, but these are wholly incorrect, as many must have noticed. A garden becomes a park. The farther part of a house is represented on so much smaller a scale than the nearer part, that the eye, accustomed to correct representations, is deceived, and imagines the farther part, by reason of its smallness, to be much farther away than it is. And thus the farther part being dragged away, the house appears to stretch much farther back than it does in reality, and consequently to be much larger. Distant objects are dwarfed down, mountains become hills, if they but stand clear of the foreground. As we see objects best at about 10 or 12 inches from the eye, this would appear to be about the best focal length for a lens. Still, as the eye does not discriminate closely in these matters, and is very tolerant with limits, lenses of all focal lengths, from 7 to 15 or 16 inches, may be employed with advantage. Beyond this, the pictures become flat and tame, and the impression of solidity is insufficient. The round pillar looks like a flat pilaster. In these cases the effect is, to some extent, corrected by removing the picture further from the eye. We can here alleviate the evil in a way that we could not with the short focus lens. Still, the effects are not good. Perspective is not without its bearing upon portraiture. All portraits taken with short focus lenses are incorrect. The nose is represented upon too large a scale for the rest of the face, because it is nearer the lens. And it is still worse with the hands and feet, if visible. If two or more persons be included, their relative sizes are not properly preserved, unless they stand exactly in line side by side. This incorrectness becomes quite striking where one person stands behind the other, and a lens of 4 or 5 inch (absolute, not "back") focus is employed. The fault in all such cases depends upon the use of lenses of too short focal length, in order to work in a short gallery, and work very quickly, 59 PHOTOGRAPHIC PERSPECTIVE. By using a lens of 7 or 8 inch focal length, and going sufficiently far from the sitter to get the reduction desired, all parts of the person will be harmoniously rendered, and the different persons composing a group will be represented in correct perspective proportion, whether near to, or at some distance from the foremost figure. , 2.-Plane Projection and Apparent Size. Plane Projection.-In the foregoing we have always considered the perspective as referred to ordinary or plane projection, that is, the surface of the image is perpendicular to the line of vision. The eye looks in the direction E C at the view A C B, which, as delineated, is supposed to be projected on the screen or paper A' B', held perpendicularly to the line of sight E. This enables us at once to fix the apparent size that any object will have in a plane projection, Fig. 62. whether it be drawn or photo graphed. For suppose the paper ,~-~ c * ~ ~to be held at one foot from the \~~~~ / ~eye, that is, that E C' is one \~~ /~ ~ ~foot. If the tree C is a hundred \~: /feet from the eye, that is, one 4\ Scu t We beg to call attention to the following specialties, for which we solicit your orders, and of which we are the manufacturers or head quarters: FENNEMORE'S SALTED COLLODION. Quick; always good; works elegantly. $2 per lb.; $1 per half lb. NOTMAN'S CANADIAN PHOTOGRAPHIC ENAMEL. Brings out the half-tones and details in the shadows: gives polish and protection to the prints. $1 per bottle. JACOBSEN'S ANILINE COLORS, for Photographs. Particularly adapt ed for Albumen Paper. Rich; brilliant; beautiful; economical. $7 50 per box of colors, brushes, &c. Sample Cartes, colored, 25 cents. BRAUN'S ELEGANT CARBON PHOTO VIEWS. Selections mailed for $5. Nothing equals them. VOGEL'S PHOTOMETER, for the Carbon process, and for regulating the exposure of the negative. $2 50. BEYRICII & VOGEL'S CARBON TISSUE, $4 perdozen. BERGNER'S PHOTOGRAPH PRINT CUTTERS. Mr. Wm. Notman, of Montreal, uses seven of them. KNELL'S PHOTOGRAPH CHAIRS AND FURNITURE. See other advertisements and send for photographs. THE AMERICAN ARTISTS' ASSOCIATION Colors for the Trade; Prints Porcelains, Solars, &c.; Copies Pictures. Patronized all over the Union. Employs the best Artists. Work warranted. CHOICE FOREIGN AND AMERICAN PHOTOGRAPHIC STUDIES. Please see advertisement in The Philadelphia Photographer, and send for List. MAGEE'S PHOTOGRAPHIC CHEMICALS. AMERICAN OPTICAL CO.'S APPARATUS. The best goods only kept. Prices low. Personal attention promptly given to all orders, large and small. EDWARD L. WILSON, JNO G. HOOD, Wf. D. H. WILSON. WILSON, HOOD & CO., 822 Arch St., Philada. 14 V0%ggf~pit 49 -t NO0. 108 NORTHF IIFTIH STREET, P1HILADELPHIA. STOCK DEALERS ONLY SUPPLIED. 15 * * w -, BENERMAN & WILSON, 41 #.tr #tt 4 ist tr t S. W. cor. of Seventh and Cherry Sts., Philadelphia, .Publishers of the Philadelphia Photographer. (See Advertisement.) In addition to the publication of the PHILADELPHIA PHOTOGRAPHER, the only live photographic newspaper in the country, we issue from our press, from time to time, such works as are required by the trade. PHOTOGRAPHIC MOSAICS, An annual Record of Photographic Progress. Edited by M. CAREY LEA, and EDWARD L. WILSON, Editor of the "Philadelphia Photographer." Cloth, $1 00; paper, 50 cents. AYRES' MANUAL OF HARMONIOUS COLORING, as applied to Photographs. By GEORGE B. AYRES. A most complete book of instruction for the learner, and a help to the experienced artist. Price, cth, $1. PHOTOGRAPHIC MOSAICS. A few back copies for sale for 1866, 1867, and 1868. 50 cents per copy, postpaid. 1869, ready 15th December. LEAF PRINTS, OR GLIMPSES AT PHOTOGRAPHY. A most complete Printers' Manual. As the leaf is the first of the tree, so is Leaf Prints the first of the great tree of Photographic knowledge. Cloth bound, $1 25. THE AMERICAN CARBON MANUAL. With specimen print. Cloth, $2. LEA'S MANUAL OF PHOTOGRAPHY. $3. 16 mtvr~a t Iti St: o5 5 toit FOR THE Painting of Photographs, MINIATURES ON PORCELAIN, ETC. A UNION OF THE BEST ARTISTS IN PHILADELPHIA. It is well understood by persons familiar with art, that the proper painting of a Photograph can only be done by accomplished artists, who, being able to draw for themselves, can make those corrections in a picture which are demanded by the faults of expression, or other defects, which are often too prominent in a mere photograph. The object of this Association is to enable Photographers all over the country to secure a talent in the finish of their pictures which they could not otherwise obtain, and which would surely increase their trade for fine work. Satisfaction is guaranteed in every case, and parties may feel assured of the work being done as well as if under their own supervision. PUORULAIN PICTURES, PHOTO NINIATURES, ETU. Many refuse to make these beautiful pictures on account of the trouble they meet with in them, and having no one to color them. This Association pays especial attentionl to this class of work, both colored and uncolored. The plain work is made on anll albumen surface by an unfading process peculiar to this Association. DIRECTIONS For Porcelain Work, send a negative of proper character, with full directions as to dress, complexion, eyes, &c., and invariably a sample of the hair. Pack the negatives with great care in wooden boxes, and prepay express. For other work, the paper prints must be sent, or in case of Solar Printing, the negatives. Also, explicit directions for coloring. When the prints are copies from other pictures, the original should in all cases be sent. The ScuIEDUIaE OF PRICES has been arranged with a view to allow a liberal margin of profit to all in the trade, whose customers can appreciate the work of real artists. A copy will be mailed on application. American Artists' Associatioii, WILSON, tOO)D & CO., Btrsi.tcsst e i]tag'ers, s22 Arch Street, Philadelphia. 17 0:I=: TLIS- TIrADEI Address, For Views and Copying. Although only the short period of two years has elapsed since this lens was first introduced it has already become widely popular, and its excellent qualifications well established, which are pre-eminently as follows: Width of visual angle, ranging from 800 to 90~; depth of focus; extreme sharpness over the whole field; true perspective; freedom from all distortion in copying; portability and cheapness. Each mounting is provided with a revolving Diaphragm, containing the stops of the different combinations for which they are designed. The larger ones are provided with an internal shutter for making and closing the exposure. No. 1, 21- inch focus, 3 x 3 plate,. $20 00 No.1 and No. 2 combined,.. $33 00 " 2, 3- " " 4 x 5 ". 2500 2 3.. 4000 3 4 " 55 00 3, 5- " 6- x 8-". 30 00 4 5 75 0 4, 8 " 10 x 12 ". 42 00 5" " 6 ".. 110 00 " 5, 12 " " 14 x 17 ". 60 00 1, 2, and 3.. 48 00 6, 18 " " 20 x 24 ". 90 3, 4, and 5.. 88 0 34,and 5 "..88 0 0 No. 3, with large mounting to combine with No. 4 and No. 5, $35. No. I and No. 2, specially adapted for Stereoscopic Views, are furnished in matched pairs. No. 1, single, not to combine with other sizes, $36 a pair. This size is constructed for special caces where the largest possible angle is required. Lenses and mountings to form all six combinations, from 2- to 18 inches, $173. entmayer's Stereoscopic Outfits. Knowing that many Photographers are retarded from making stereoscopic views on account of the high prices heretofore charged for lenses, thus depriving them of what might be a source of considerable revenue, I take pleasure in announcing that in order to obviate this, I offer a Stereoscopic Outfit, consisting of I pair 3- Focus Lenses, best quality, in mounting not to combine with other sizes. I American Optical Co.'s Stereoscopic Box, 4 x 7, made especially for these lenses. 1 Folding Tripod for box. 1 7 x 10 Tight Covered India Rubber Bath and Dipper. 2 4 x 7 American Optical Co.'s Printing Frames. The whole, except the tripod and printing frames, contained in a neat box, with handle, convenient for carriage, and weighing only 11 pounds. PRIiCE, COMPLETE, $60. Nothing ever offered can compete with this outfit either in price, quality, or cozvenience. This should enable every photographer to make first-class stereoscopic work. Orders by mail will receive prompt attention. For further particulars, please address JOSEPH ZENTIAYER, 147 South Fourth Street, Philadelphia, 18 -g'6 C77gLESO WILLARD MANUFACTURING CO.'S CELEBRATED CaMER TlU —3S AN'D FOR Portraits, Views, Copying, Gems, Stereoscopes, &c, &c,, Which received the Highest Premium at the late FAIR OF THE AMERICAN INSTITUTE. We have received nearly 500 Letters of Reoin cLation in favor of their excellent qualities and superior workmanship, and can safely recommend them to be superior to any other make in use. Price List mailed to any address. FOR SALE BY Stock Dealers throughout the United States and Canada. WILLARD MANUFACTURING CO.'S PHOTOGRAPHIC AND OPTICAL DEPOT, 684 -roacdway, NEW YORK. 19 -s 500 500 THE DALLMIEYER LENSES. For Price List and full Description of the various Styles and Sizes of these Valuable Lenses, apply to E. & H. T. ANTHONY & CO., 501 BR OAD IVA N, AE W YORK, SOLE AGENTS FOR THE UNITED STATES. ~_-~ The splendid Stereoscopic Views of Wm. England and G. W. Wilson are made with Dallmeyer Lenses. All Stereoscopic Photogra phers should have them. >r The beautiful Cabinet Card Pictures of the White Fawn, by Gurney & Son, are made by a 3 B Patent Quick-Acting Dallmeyer. We subjoin a few extracts from the numerous unsolicited testimo nials we have received from our customers. lIr. A. D. DEMING, Oil City, Penn., writes:-" The Dallmeyer Tube continues to give entire satisfaction. Scarcely a customer that has Cartes de Visite taken with it but what duplicates the order at once on receiving the first lot. The standard of my work has been improved very much by having such a good instrument to operate with, which of course in due time will increase my business in the same proportion." From S. B. RUSSELL, Navasota, Texas, July 17, 1868. —" My work is increasing double since I received the Dallmeyer Lens. It is the cheapest of all instruments. One artist has tried mine (No. 2 B), and is determined to have one at once." From J. F. RYDER, Cleveland, 0., May 14, 1868.-" I have to say in favor of the Dallmeyer Lens that it improves on acquaintance. The longer I have it, the more I prize it." From G. D. WAKELY, Washington, D. C., April 28, 1868.-" The pair of Dallmeyer Lenses you sent me are very fine. They are the most useful instruments I have." From H. ROCHER, Chicago, Februarv 5, 1868.-" I have used since July,'66, a Dailmeyer No. 2 B, and am perfectly delighted with the beauty of work made with it. Nothing satisfies me but the very best. I find this to be the best principle, for I command here the highest prices for my work." From J. S. BROADWAY, Charlotte, N. C., Sept. 8, 1868.-" I like the Dallmeyer ILenses very much. They are increasing my business considerably. I think by their use I can increase my business double." From FRANEKLIN WHITE, Lancaster, N. H., Sept. 8, 1868.-" The 3 D Dallmeyer which you sent me is a splendid one. It is a pleasure to use it." The truest ECONOMNIY is to use the best lenses. 20