OD! the (coie b-IQd: file OF )P~otog#pa17it 4ei\r, BY I. " β€”. )ALLMEYER. REPRINTED AND PUBLISHED BY -E. & H. T. ANTHONY & CO.. NEW YORK. 1874 Oi t~he 4hoiCe hrAd Itfe OF oto'o-iipI' iel e, BY J. H- DALLMEYER. REPRINTED AND PUBLISHED BY E. & H. T. ANTHONY & CO., NEW YORK. 1874. PORTRAIT LENSES. SUCCESS IN PORTRAITURE will always depend, in a great measure, upon the iizghlt c/oice and the propaer 2tse of the lens. A few hints on these two points may prove of service to the photographer. Portrait lenses are either more or less rapid in action as their diameters are larger or smaller, or as their focal lengths are shorter or longer. The diameter of a lens here always implies its actzta[ working aperture, and the focal length, its euivalernt focal length. Directions for ascertaining these are given in the appendix. The focal length of a lens regulates the size of the picture, and the diameter expresses its speed or rapidity of action. Having fixed upon the size of picture required to be taken, the next thing to be determined is the most suitable focal length of the lens. This, however, involves the 4 prior determination of the distance at which to place the subject; for, as every photographer knows, the placing of the lens nearer to the subject increases the size of the picture, and vice versa. The question then arises, -What is the proper distance at which to place the subject from the lens? In answer it may be safely asserted, that it should, as a rule, be not less than i2 feet, nor perhaps more than 24 feet. For if less than this, the resulting picture will generally be defective both in definition and perspective, because the lens producing it will be of too short a focus; and if the distance is greater, the resulting picture will probably be deficient in relief or roundness. This, because the atmosphere in our towns is seldom quite clear from fog or haze,* and the greater the distance between the lens and subject, the more obviously will this haze be reproduced in the picture. A medium distance, therefore, of from I6 to 20 feet, should be chosen. Card portraits are generally taken with lenses of such focal lengths as to require this distance, and to this circumstance may be attributed the generally pleasing appearance of these portraits, as compared to the old quarter plate pictures, which were mostly taken with lenses of much shorter focal lengths. * The writer refers, of course, to towns in England. 5 For a distance, then, of from i6 to 20 feet between the lens and subject, the equivalent focal length (not the back focus) of the lens, for a given sized plate, should be about twice that of the largest side; that- is, for a 41 X 31 plate, the card size, the focal length should be 41 X 2, or equal to 81 inches, i. e., No. 2 B Lens; for a 6 X 5 plate, the cabinet size, 6 X 2, or equal to I2 inches, i. e., 3 B, 2 A, or better still, 3 A Lens; for a IO X 8 plate Io X 2, equal to 20 inches, i. c., 4 A Lens, and so on. In confirmation of this, I may mention that the much admired Io X 8 pictures of M. Adam-Salomon are taken with a 20 inch focal length lens. The distance between the lens and subject here given requires a studio of at least 30 feet in length; and photographers who have not this space are compelled to use lenses of shorter focus, such as the I B [long] or I B for -cards, and the I A for cabinets; but they labor under disadvantages, as regards instrumental aid, which no amount of skill can possibly compensate. IIaving determined the focal length of the lens for a g'iv.en sizedplate, the next thing requiring consideration is its diameter, or its rapidity of action. As a matter of course, every photographer wishes to possess a quick-;cting lens, and not only this, but flatness of field, andt great 6 " depth" of focus or definition, forgetting all the while that these qualities are almost diametrically opposed to each other; for rapidity can only be had at a corresponding sacrifice of flatness of field and depth of definition. Thus, of two lenses of the same focal length, and both perfectly corrected for spherical aberration, the one of 2 inches will have twice the depth of another of 4 inches in diameter; whilst the latter, in turn, is four times quicker in action than the former. Again, of two lenses of the same rapidity (i. e., having the same ratio of aperture to focal length), the one double the focal length of the other will only have one quarter its " depth." - Thus, for example, a card lens of 9 inches focal length and 2j in. aperture, producing a card picture at 20 feet distance, will sufficiently define accessories 12 inches in front and I2 inches behind the figure, or the point focussed upon, or will have a depth of 2 feet; whereas, another lens of double the above dimensions, i. e., of I8 in. focus and 5~ ins. aperture, and worked at the sam~ze,distance, will only have a depth of 6 ins., viz., 3 in. before and 3 in. behind the point focussed upon. This sufficiently explains that really quick acting lenses only produce satisfactory results when used for the smaller sized plates; but that they are useful, when so restricted is suf 7 ficiently evidenced by the charming instantaneous portraits of children by Mr. Faulkner, Mr. H. C. Heath, and others, taken with No. 2 C-perhaps the quickest acting lens extant. For standing figures this lens requires stopping down, as explained in my Catalogue. Hence the quick acting, or B Lenses, are only made for plates up to 8~ X 6-. For larger pictures slower working lenses, capable of adjustment for diffusion of focus, are the only means for securing the requisite amount of depth of focus. It may be stated here that for every-day work, for whole plate Portraits and beyond, perhaps the Patent A Lenses are the most suitable. Thoy are ne-rtlv twice as rapid in action as the D Lenses; of great importance considered from a commercial point of view foi long exposure very often occasions "a failure. Hence nearly all the first artists, as for instance Messrs. Blanchard, Briggs, Heath, Mayall, Mayland, Robinson, Slingsby, Wane, and others, constantly use these lenses for the ordinary demand of portraits; but for their extra size pictures, as for instance for those recently exhibited, the first-named artist uses No. 5 or 6 D.; Mr. Slingsby a No. 7 D.; and Mr. Crawshay, for the largest portraits, perhaps, ever taken direct, a No. 8 8 D. Col. Stuart Wortley's large portraits were tavcen with a 22 X 20 Rapid Rectilinear Lens. Thus much respecting the right choice of the lens; and now a few words regarding the proper use of it. The lens, when attached to the camera, should be placed upon afirrn stand, capable of adjustment as to height etc.; the cap should fit the lens loosely, so that its removal does not occasion tremor, or shaking of the camera. Cap the lens, and, protected by the focussing-cloth, carefully examine the interior of the camera to insure a perfect dark chamber. No bright object, such as the unblackened head of a screw, or a bright brass spring on the shutter, should be tolerated anywhere. The wood of the interior of the camera, also, should be coated with a dead, and not a shining, black varnish; and, better still, a number of dia. phragms, according to the length of the camera, should be introduced, allowing the full cone, or pencil of light, proceeding from the lens, to fall upon the prepared plate uninterruptedly, cutting off all reflections from the sides of the camera. The larger the diameter, or the more rapid the lens, the greater the importance of the above remarks. Always carry the slide containing the prepared plate under a focussing-cloth to the camera, and let this cloth remain on it when drawing up the shutter. 9 Now proceed to test the camera as to regi'ster. At a convenient distance place a sheet of newspaper or other clear print; carefully focus for this on the screen. (A focussing glass, such as a Ratmsden eye-piece of about I or xi inch focus, adjusted upon the greyed surface of the ground glass, should always be used for this purpose.) This done, remove the screen, and replace it by the collodion slide; but, instead of introducing the sensitized plate, put into the slide a piece of ground glass, ascertained to be perfectly flat. Now observe whether the image appears as sharp on this dts it was previously on the screen; if so, the camera is correct, or what is technically called in "register;" if the image is not sharp, the position of the ground glass requires to be altered ulnti it ik; so.. The common practice of reasazring by means of a rule the distance between thie camera front and screen, and then between the front and prepared plate in the colocldion slide, is quite inadequate to insure the necessary accuracy, especially for quick-acting lenses. Care should also be used in the selection of the glass for the negatives, for it will be found that, even of the patent plate, the percentage of really flat glasses is but small, -more especially among the larger sizes. Another source of error frequently exists in a too pow IO0 erful spring on the door of the dark slide. This, when too strong, causes a bending of the prepared plate in the centre, and, unfortunately, this bending is just in the opposite direction to that required by the slight curvature of image as produced by all lenses. Thick plates are, of course, less liable to bend than thin ones; but to be quite rid of this possible source of error, remove the onze strong spring from the centre of the shutter, and replace it by two weaker ones, made to press equally on the two sides of the plate. Lenses are sometimes blamed for non-coincidence of foci, when the fault is really an imperfect camera, or defective glass plates; it is hoped, however, that a little attention to the above will at once satisfactorily determine this pQo[t: As regards the best position of the camera, a few hints may be of advantage, especially when it is required to take a standing figure; for no lens gives a perfectly flat field; and hence the placing of the camera requires great care, in order as much as possible to favor the action of the lens. For a card portrait, using No. 2 B Lens, distance of subject Is feet, the camera being without a swing back, arrange as follows: Height of centre of lens from the floor, about 4 feet io inches; rising front of camera elevated I inch; let the I I image occupy the centre of the plate-i. e., the head and feet equidistant from bottom and top of screen. To effect this, the camera requires tilting forward slightly. (Tilting the camera forward is an advantage, for it produces'a more natural view of the face, and is preferable to its being placed lower and level, which latter position implies a looking sp into the face, and produces neither a natural nor pleasing picture.) The image occupying the centre of the plate, proceed to focus for the eye, and then for the chest, or for some prominent object on the chest, as a watch chain for instance; now halve, as it were, the focus between this and the eye, when it willI be found that tile resulting picture will be evenly defined throughoutt its entire length. The above is the actual not o7ls qperalzdi of one of our ablest portraitists, to whorm I an indebted for the particulars. For the cabinet portrait, standing figure, using No. 3 B, 2 A, or 3 A lens nearly the same conditions obtainu; and hence the camera should be placed in tile sanme position. Photographers cv/l/tei2ek on account of insufficient: length of studio, to use shorter focus lenses tllan the above -viz., a No. I B or I B long, for cards, and. Noat: A, for 12 cabinets, should use the utmost care in adjusting the position of camera, for the use of shorter focus lenses implies a larger angle of definition. The above should be modificd thus: Height of centre of lens from floor, 4 feet 8 inches; rising front, elevated X to 3-x6ths inch; the rest as before. A sitting figure requires the camera to be placed at a somewhat lower level, and here a swing-back to the camera is of great advantage. Indeed, portraits beyond the halfplate size should never be attempted without this adjunct; for, as stated already, the longer focus lenses are much more sensitive to any difference of distance than are the shorter focus ones, and in a sitting figure the feet are often as much as 24 inches in advance of the face. This occasions nearly -1 of an inch of difference in the focus of a 20 inch lens. Hence, without a swing-back, allowing the top of screen or slide to be inclined outwards that distance, definition of the feet and legs simultaneously with the face is almost impossible. In placing the accessories of a portrait, or in disposing the positions of a group of persons, regard should always be had to accommodate as much as possible the curvature of field produced by the lens; and this is accomplished by arranging the group or accessories in approximation to a curve. That is, objects at the sides should be brought 13 nearer to the lens than those occupying the centre; the image then falls on a plane, and this is what is required. The amount of curvature of field varies in different lenses, and hence definite rules for placing the objects composing a picture to suit this curvature cannot be given, but one or two trials will at once determine this question. One other point remains to be noticed; it is this. A photographer accustomed to work with a short focus lens, and exchanging this for another of longer focus for the same sized plate, often complains of a want of brilliancy or roundness in his pictures. Now, in almost every instance, this is simply a question, not of lens, but of lig/ltitug', for a little consideration will make it apparent that the direction and amount of light suitable for a subject at a distance of I2 feet, requires considerable im-odification, when the distance is increased to 20 feeto Then as to the time of exposure required by a lens-a question so frequently asked, but one which involves so many elements, viz., aperture of lens, lighting, clemnicals, etc., that it is impossible to give a definite answer. i%- currect reply can only be given re/ilatzley; that is, if the tine of exposure for a certain class of lens is known, then another kind of lens will require so much maore or less, as the case may be, according to its construction. This information . I4 is to be found in my catalogue, where the lenses are classified according to their respective rapidities. If nothing relatively is known, then one or two experiments with the full aperture, of the lens in question, is at once the readiest way to determine the point; and when ascertained for the full opening, the rule for finding it for any smallersized. stops is given in the'catalogue. VIEW LENSES. THE right choice among the many existing forms of view lenses requires the determination of the following points: Ist. The size of the picture. 2nd. The angle of view, or amount of subject to be included in it. 3rd. The kind of picture, whether landscape, or architectural, or both.',.,gards the first point, viz., "the size of picture," the professional photographer needs no information β€”he being guided by commercial considerations-but a few remarks addressed to the amateur on this liead may be of service. The beginner will find a small sized plate, such as a 71 X 44 up to IO X 8 in., quite sufficient, being convenient for practice, and enough for producing artistic effects. The former of these sizes has the advantage of being adapted alike for a stereoscopic, or for one single, picture. In recommending the smaller sized plates, it may be well to remind the amateur that not only do the difficulties of manipulation greatly increase with any increased dimensions of plate, but that the quantities, weight, bulk, etc., of all the other necessary appliances become augmented also, and this in the proportion of more than the square for every increase in size of plate. Secondly, "The angle of view" to be included in the picture. This depends upon the relation of its size to the focal length of the lens; that is, the shorter the focus the larger the angle, and vice versa. The base line, or the longest side of the picture, is the measure of the angle included in it. One of the principal and rightful claims of photography is its perfect truthfulness of delineation; and yet, how frequently do we meet with pictures representing well-known objects or scenes, which at first sight are not even recognized! This fact has been observed more frequently of late, since the introduction of the wide-angle, or short-focus lenses. The cause of these apfiarentlhy dis torted views really turns upon the amount of angle included. in them, and hence there arises the question, What is the proper amount of subject, or angle, to be included in a picture? The reply to this necessarily involves a consideration of the laws of perspective β€”a subject well worthy the attention of every photographer. The following two propositions are sufficient for -nmy prevent purpose, viz.: That the human eye itself is a miniature photographic camera, inasmuch as the several rays proceeding from objects, upon entering the eye, are refracted by its lens, and thence proceed to form a most perfect image or picture on the smooth screen of nerve called the retinza; and that it is by this picture that the mind is enabled to judge of the dimensions, brightness, color, etc., of external objects. The angular extent of the picture formed upon the retina certainly does not exceed 60~, without some movement of the eye or head. Hence, for a photograph to convey to the mind a correct idea of the objects represented, it should, when viewed at the normal distance of from I2 to 15 inches, excite the same impressions. Now the distance at which a picture is generally viewed will be found to be about equal to- its base, or longest side; or, in other words, the angle it subtends for I7 vision will be from 500 to 60o. This angle, therefore, should not be exceeded, for if more is included in the picture, the perspective will appear exaggerated, i. e., objects in the foreground will be too large, and the distance become dwarfed. To render it obvious that distortion of this nature is really no fault of the lens, when such pictures are viewed at a distance equal to the focus of the lens with which they are taken, all apparent distortion at once vanishes. This rule holds good in all cases, i. e., every picture should be viewed at a distance equal to the focal length of the lens with which it is taken. Thus a 12 X Io picture taken with a 7 in. focus wide angle Rectilinear Lens should be looked at, not at I2 or I5 inches, but at 7 inches distance from the eye. From the above it is obvious that the only legitimate use of wide angle lenses is landscape photography; or, in other words, for that class of subjects in which absolute truth is subservient to beauty; but for architecture, and the like, such lenses should be used only in case of necessity-i. e., when the situation is so co'filzed as to preclude the use of a longer focus lens. As regards the choice of a lazdscape lenzs, all the most eminent landscape photographers are unanimous in recom. mending the "'single combination " for simple landscapes, for the obvious reason that this lens, having but Iwrj reflecting surfaces, the rest being cemented, produces the most brilliant pictures; and, on account of its form, it has more depth of focus than a double combination lens. Further, the wide angle single combination landscape lens produces an evenly defined picture with a comparatively large stop or aperture. Hence, it is more rapid in action than the wide angle double combination lens, which it surpasses, moreover, in equality of illumination throughout the entire extent of the picture. The only drawback to this form of lens is a slight amount of perceptible distortion when used for objects bounded by straight lines, such as architecture, where the marginal lines will be slightly curved. Hence, to avoid this, in a landscape with buildings, the latter should not be made to occupy the extreme margins of the picture. Among the several kinds of single'combinat.ion view lenses extant, other things being equal, the smallzer its diameter, the better the lens. As regards focal length, it has already been stated this should not be less than the base line of the picture; that is, for a Io X 8 inch plate, a Io inch focal length lens, rather longer than shorter, should be chosen. The profession al photographer desiring the best possible results must necessarily be provided with two or three lenses of different focal lengths for the same size of plate, so as to suit' his lens. to his subject; and this is really the practice of all our best photographers. Thus I may mention, that for Mr. G. W. Wilson, of Aberdeen, I made as many as five pairs of different lenses for his stereoscopic pictures, viz., three pairs of quick-acting single combination landscape lenses, of 41, 6, and 8 inch focus, respectively, and two pairs of wide angle Rectilinears of 3 and 4 inch focus. Mr. England uses similar lenses for his stereoscopic pictures; and for his well known 9 X 7 Swiss views he employs as many as five lenses, as occasion requires, i. e., from 5- up to Io or 15 inch focus. Mr. F. Good and others adopt the same practice. For archilecture, a rectilinear lens must, of course, be chosen, and for general use, one of moderate angle is to be preferred. The Rapid Rectilinear is the best lens for that purpose, as it is free from distortion and flare, and works with a larger opening than any other kind of double lens. It is invaluable, therefore, for dark interiors, instantaneous effects, etc. Mr. Bedford has produced the most charming pictures with this lens, both of interiors and landscapes with buildings. 20 For special purposes, as for objects in confined situations, the wide angle Rectilinear lens becomes indispensable; but here it may be observed, for the reasons already given, that it should be used only in cases of necessity. More than ordinary care, moreover, is requisite in the adjustment of the camera when wide angle lenses are used. The camera should always be placed perfectly level, and, if required, the rising front should be used; but on no account should the camera be tilted, for, in that case, perpendicular lines of objects will no longer appear perpendicular in the picture. If, however, the camera must be tilted, then a swing-back becomes indispensable, in order to restore parallelism between the object and the screen, or collodion slide-always a necessary condition for the production of a picture free from distortion. Observe, it is the better plan not to tilt the camera, but, if more is required in the picture, to raise the camera-front or to get on higher ground, if practicable. Of double combination lenses, that one is always to be preferred which, with the smallest diameter of lenses, really works with the largest aperture or stop, and covers the widest angle. [See my paper " On the Cause of the Central Spot or Flare " in the Phologroaplhic ournal, June I5th, I867.] If a lens is required for geeteral ptfurposes, as for land 21 scapes, architecture, instantaneous views, groups and portraits in the open air, then a double combination lens must be chosen; and for out-door work of this kind, I have no hesitation in stating that the Rapid Rectilinear is the best lens an amateur, or even a professional, photographer could fix upon. All the instantaneous views by Mr. Robinson, Col. Stuart Wortley, and others, were taken with the Rapid Rectilinear lens; and the latter gentleman has even succeeded in producing his large portrait studies with the same instrument. But for portraits in the stuZdio it is scarcely sufficiently rapid in action, and if it be the aim to combine this and landscape photography, etc., in one and the same instrument, then a D Patent Portrait Lens will probably best fulfill the several requirements. For copying purposes, the Rapid Rectilinear Lens is without a rival. It has already been supplied to all the Government topographical establishments in Europe, India, and Australia. The two combinations composing this lens being perfectly identical, it is alike suitable for copying of equal size, or for reducing or enlarging. One or two remarks about the proper use of a view lens, when the choice has been made. In the selection of a view, always aim as much as pos 22 sible to favor the natural curvature of field as produced by the lens, i. e., if possible let the side objects be nearest to, and the centre ones farthest away, from the camera. When photographing a flat object, as a block of buildings, or when copying a map or plan, focus for a point onethird from the centre, and the resulting picture will be approximately equal in definition throughout. Always work with the largest possible aperture or stop, if you wish to secure relief and atmosphere in your picture. Proceed as follows: Focus for t/Se object, i. e., that which is to constitute the point of interest in the picture, and which is generally near in the foreground; do this with a medium stop; when done, look to the distance and other objects in the picture, and only reduce the aperture just so much as will prevent these appearing foggy. But do not aim at equal sharpness everywhere, if you wish to produce a pficture. For what artist would think of painting his background or accessories as sharp in outline as the subject of his picture? And who ever saw the distance perfectly sharp in nature when the eye is adjusted upon some object near in the foreground? Photography is claiming higher ground than the old standard of excellence, viz., sharplsess everywhere; and those who aim at artistic photography may find the above hints of some service. 23 As regards the best kind of camera suitable for view lenses, that with the bellows body is the most convenient being portable, and, when well made, answering every purpose. Among these, perhaps, the square bellows body camera is preferable to that of the conical, or Kinnear form, inasmuch as the former can be used for lenses of very short focus, whereas the latter, when used for such lenses, frequently intercepts a portion of the cone of rays, and spoils the picture. For directions of testing the camera, etc., see remarks on this subject under the heading "Portrait Lenses." APPENDIX. To find the anzgle of vieze, or the amount of subject included in a picture, ascertain the equivalent focus of the lens, and measure the base line of the picture. Upon a sheet of paper draw a line of the same length as the latter, bisect it, and let fall a perpendicular exactly equal in length to the equivalent focus of the lens; join the extremity of bisected line and perpendicular by another line; now apply a protractor, and measure the angle included between these two lines, and the angle read off, multiplied 24 by two, is the angle included in the picture. Or, with the data known as above, and a table of natural sines and tangents at hand, divide half the base line of the picture by the equvialent focus of the lens; find in the tables under the heading " tangents " the same ciphers as the above quotient, and the corresponding angle, multiplied by two, is the angle included in the picture. The following particulars may be of service: If the base line, or the longest side of the picture, is equal to the equivalent focus of the lens, the angle included is 530; if the base line measures -I~ the equivalent focus, the angle is 640; if I it is 740 ~; i I it is 82~; if twice it is 900. Depil/ of focus, or depth of definition, is dependent upon the aperture and the focal length of the lens. It increases in the same ratio as the diameter of the opening or aperture is reduced, and it diminishes as the square for any increase in the size of picture, or the focal length of lens. IHence, the shorter the focal length, other things being equal, the greater the "'depth," or the nearer may be an object in the foreground; beyond which everything else will be in practically good focus. The rapidity of a lens depends upon the relation or the ratio of aperture to the equivalent focus. To ascertain 25 this, divide the equivalent focus by the diameter of the actual working aperture of the lens in question; and note down the quotient as the denominator of a fraction with I, or unity, for the numerator. Thus, to find the ratio of a lens of 2 inches diameter and 6 inches focus, divide the focus by the aperture, or 6 divided by 2 equals 3; i. e., ~ is the intensity ratio. Another lens, of 4 inches diameter and 24 inches focus, has I-6 for its intensity ratio; and this ratio once ascertained, it only remains to multiply each denominator by itself to find their comparative rapidities. As above, the ratio of the 2 in. lens is ~, or 3 X 3 equals 9; the ratio of the 4 in. lens is I-6, or 6 X 6 equals 36: therefore, if the 2 in. lens requires 9 seconds exposure, the 4 in. lens necessitates 36 seconds; or, in other words, the 2 in. lens is four times quicker acting than the 4 in. It must be observed, however, that in order to find the real intenzsity ratio, the diameter of the actual working aperture must be ascertained. This is easily accomplished in the case of single lenses worked with front stops, or for double combination lenses used with the full opening, these merely requiring the application of a pair of compasses or rule; but when double or triple-combination lenses are used, with stops inserted betweenz the combina. 26 tions, it is somewhat more troublesome; for it is obvious that in this case the diameter of the stop employed is not the measure of the actual pencil of light transmitted by the front combination. To ascertain this, focus for a distant object, remove the focussing screen and replace it by the collodion slide, having previously inserted a piece of cardboard in place of the prepared plate. Make a small round hole in the centre of the cardboard with a piercer, and now remove to a darkened room; apply a candle close to the hole, and observe the illuminated patch visible upon the front combination; the diameter of this circle, carefully measured, is the actual working aperture of the lens in. question for the particular stop employed. The operation must, of course, be repeated for any other sized stop that is inserted between the lenses. It would be of great advantage to photographers generally, if, in the description of experiments, etc., the above -zntenzsity ratio were always recorded, as it is the only real standard of comparison between the rapidities of different lenses. The back focus of double-combination lenses, as,'for instance, of a portrait lens, depends upon the separation or interval between the two combinations; it is, -therefore, a variable quantity, and cannot be taken as a:measure 27 of comparison between lenses of different construction. The true standard of comparison for double or multiple combination lenses is what is termed the equir'aicntfocu, or the equivalent focal length, viti, that quantity, or leg.-th, which is equal to the solarf octts (or the focus for parallel rays) of a thin single lens, such as a spectacle eye lens. HIence the name equivalent focus. Since, however, the size of an image produced by any lens is always in exact proportion to its equivalent focus, the latter can readily be determined, if the former is known and vice versd. To judge, then, of the comparative focal. lengths of any two lenses we have only to place them side by side and to compare the size of their respective images, both pointing to the same object. For example: A spectacle eye lens has a solar focus of exactly io inches, and the size of image produced by it of some distant object measures 4 inches in height; the same object focussed upon with a portrait lens measures 8 inches on the screen. Required' the equivalent focus of the portrait lens. Then, by simple proportion, as the size of image of the one is to that 6f the other, so also are their foci, or as 4: 8:: Io: 20 inches, the eitzivalentfocus of the portrait lens in cquestion. The above method affords a ready means of comparing 2$ the relative focal lengths of different lenses when placed side by side; but to arrive at the absolute equivalent focus of a given combination is somewhat more troublesome,'and involves the possession of a single lens, the solar focus of which has to be measured with great care. There is, however, a readier mode for ascertaining the absolute equivalent focus of any combination lens, and this, with sufficient accuracy for almost every purpose; besides which, no adjunct is required, other than that in the possession of every photographer. It depends upon a law in optics; namely, that when the size of the image produced by a lens is exactly equal to that of the object, then the distance between the object and the focussing screen measures exactly four times the equivalent focus of the lens. To find the equivalent focus of a given lens, proceed as follows: Take a flat piece of wood, as a drawing-board, with a piece of paper stretched upon it, place it before the camera, and adjust it at right angles to the lens in two planes, as is customary for copying pictures or maps. Draw two lines at right angles to each other upon the paper, and see that the point of intersection coincides with the axis of the lens and the centre of the focussing screen. On each side of the centre of one of the lines, measure and mark off with a pair of compasses a certain distance, equal to about one-fourth of the base line of the focussing screen. Now proceed, as in copying, for equal size or scale, i. e., adjust the distance between lens and object, and lens and screen, until the image of the mapped line on the screen, whenZ sharply defined, is exactly equal in length to that on the paper. The pair of compasses already made use of answers the purpose. Now remove the lens, and carefully measure the distance between the paper and the focussing screen; and one fozrth of this distance is the equivalent focus of the lens in question. The approximate opticalcentre of the lens can be determined at one and the same operation. For this purpose, replace the lens, without altering the arrangement, and make a mark upon the mounting or tube exactly equal to one-half the distance between the paper and focussing screen, measuring from the former. This point marked upon the lenstube indicates the optical centre of the combination, and is, in fact, the zero from which to calculate or to measure the distance of the object, and the focussing screen, either for enlarging or reducing to a given scale. To find the exact positions of the object and the focussing screen, both measured from the optical centre of the lens, for a given enlargement, add I to the number of times you wish to enlarge, which, multiplied by the focal length 30 of the lens, gives the position of the focussing screen, or indicates the required length of the camera; and this length divided by the number of times of enlargement gives the position of the object that is to be enlarged. Thus: required to enlarge a 5 X 4 negative four times (i. e., to 20 X i6 inches), with an 8 inch equivalent focus lens; then to 4 + I, equals 5, multiplied by 8, equals 40 inches, or the length of the camera or position of the focussing screen; and 40o divided by 4 equals Io inches, the distance at which to place the negative from the optical centre of the lens. For reducing, the positions of object and focussing screen are as follows-add r to the number of times you wish to reduce, and multiply by the equivalent focus of the lens,. the product gives the distance of the object from the:lens; and this, divided by the number of times you wish to reduce, indicates the position of the focussing screen, or the length of the camera. In the above example we have only to change the place of object for the screen, and vice versa, when the positions are correct for reducing to i scale. In copying transparencies, carefully guard against any other but paralZel rays being made use of for the formation of the image. To effect this, place a parallel box of light wood or paper projecting a considerable distance in front of the transparency; the box should be blackened 31 inside, or, better still, lined with- velvet, or provided with several diaphragms with openings of the same size as the transparency. Always endeavor to.shade the lens as much as possible, i. e., keep from it all extraneous light not actually used for the formation of the image, and the resulting picture will have its brilliancy proportionally augmented. This remark applies more especially to double or multiple combination lenses. The glasses composing a lens should be free from veins, strie, etc., and the several surfaces should be well polished by the optician; any remaining dull or grey appearance after careful wiping indicates defective polish. The presence of a few air bubbles does not in any way affect the performance of a lens; but, unfortunately, everyone can see these, whereas other defects much more serious can only be detected by a practiced eye. The more limpid or colorless the glass, the better the lens. The fewer the number of reflecting surfaces, other things being equal, the greater the brilliancy of the resulting picture. The smaller the diameters of double combination lenses, and the nearer that they are placed together, other things being equal, the greater the freedom from flare. 32 Keep the lenses as much as possible in a dry atmosphere, and guard against sudden changes of temperature, otherwise some kinds of glass are liable to tarnish, or what is technically termed to "sweat. " Whenever any moisture becomes visible upon any surface, at once remove it by wiping with a soft cambric or old silk handkerchief; otherwise resort to wiping onli when particles of dust adhere so firmly to the glass that they cannot be removed with a camel's hair-brush. Never attempt to polish the lenses with any kind of powderwhatever. THE END, THE THE'GREAT CENTRAL.''GREAT CENTRAL.' Ch.sm WM. Stevens, Photographers' Supplies, LARGEST STOCK. LOWEST PRICES. PROMPTEST HOUSE IN THE WEST. i158 ST/ATE ST TREET, obbr 111 10 2 ultoil, 228 SUPERIOR STREET, CLEVELAND, O., WHOLESALE DEALERS IN PHOTOGRAPHIC GOODS, APPARATUS, OVAL AND SQUARE FRAMES, MOULDINGS, CHROMOS, ENGRAVINGS, PASSEPARTOUTS, MATTS, ARTISTS' MATERIALS, ETC., ETC. ALSO, MANUFACTURERS OF THE BEST MADE AND MOST PERFECT WORKING IN THE WORLD. Satisfaction Guaranteed in Quality of Goods, Prices, and Promptness in Filling Orders. Photographic Furnishing House for Texas, BLESSING & BRO., 174 TREMONT ST., GALVESTON. KEEP A FULL SUPPLY OF FRESH PHOTOGRAPHIO and FERROTYPE APPARATUS, STOCK and CHEMICALS, From the most roliablo Manufacturors and Importers. Lenses, Diamonds, Plates, Camera Boxes, Evaporating Dishes, Genuine B.P.C. Glass, Gem Cameras, Mortars & Pestles, French Glass, Stands, Funnels, Porcelain Plates, Baths, Collodion Vials, Card Mounts, Trays and Pans, Graduates, Card Board, Printing Frames, Backgrounds, Gem Mounts, Negative Boxes, Head Rests, Paper Matts, Posing Chairs, Union Goods, Standard Matts, Scales & Weights, Cases, Frames of all kinds, Picture Cord and Nails, Stereoscopes and Views, FROM TWENTY-FIVE CENTS TO TEN DOLLARS EACH. Papers, Morgan's, Trapp & Muiinch, S. & M. Dresden, Swiss Pink. Filter Paper, Adhesive Paper, Atwood's Alcohol, Ether, Collodion (Blessing & Bros.' is always fresh and none better), Iodides, Bromides, Silver, Varnishes, etc., etc. In fact everything kept in a first-class furnishing house.; Send your orders to us and save freight and annoyance. All Apparatus and many other goods at manufacturers' prices. no SEND FOR PRICE LISTS..d3 Agent for the Dominion of Canaaa for the celebrated DALLKETEYM LENS. TORONTO, ONT. z'ti~t,& evelywtrtee 6tdkirzow1edge it to be the best ever ue d by t1errn. $ee tetinqoQy feonj the igtesft Utitlofity. xJeedle$i to'add otleif. MONTREAL, July I7, I869. E. J. PALMER, ESQ. Dear Sir: In reply to your favor of I5th inst., I beg to say that having for many years used Dallmeyer's lenses and found them highly satisfactory, I have no hesitation in pronouncing them the best that are in the market. I have never met with any to compare with them. Yours truly, (Signed) W. NOTMAN. THE ROSS LENS Is Unequalled for Portraits and Landscapes. THE STEIINHEIL LENS Has no Equal for Groups, Copying & Views. CATALOGUES ON APPLICATION, GRATIS. WILSON, HOOD & CO., (Sole Agentsfor the U. S.) 822 Arch Street, PHILADELPHIA, PA., ~ATCHEL & HYATT, PUBLISHERS, MANUFACTURERS, IMPORTERS, AND DEALERS IN PHOTOGRAPHIC SUPPLIES. We keep immense stocks of all desirable goods needed by the trade at our three storehouses inCincinnati, o., io8 W. FIFTH ST., St. Louis, Mo., I8 N. FOURTH ST., Louisville, Ky., 89 JEFFERSON ST. Orders filled promptly at lowest rates. Try us. -- SEND FOR PRICE LISTS. DODGE, COLLIER & PERKINS, Wholesale Depot FOR Every Article used in the Art. MA{UFACTURERS OF Frameos, Moldings and Storooscopos, IMPORTERS AND PUBLISHERS OF VIEWS, CHUOOS, ETC., ETC. Every article desired by the Picture and Frame Trade at the lowest prices. SEND FOR PRICE LISTS, Southern Photogra1hic anid Frrotyue STOCK DEPOT, CHOSSGUP &WEST.PHA Send for Price List. Saving Time, Freight, Insurance, Drayage, MILWAUKEE. c'Ysw.AvTsA.. 0 I:):, NORTHWESTERN PHOTOGRAPHIC WAREHOUSE AND COH1MICoi-L'A130BATORY, No. 11 Spring Street, Ailwaukee, Wis. A,FULL LINE OF PHE[OTOGRAPHIIC GOODS,: EMBRACING APPARATUS, CltE~IICALS, ALBUM[ENIZED P &PERS, GLASS, FRA3RIES9 ALBhUMS9, VIEWS, ETC. Nitrate of Silver and Chloride of Gold-made for photographic purposes. Gold and Silver Wastes refined. Returns made within two weeks. Satisfaction guaranteed. Send for Price List. Benj. French & Co., 159 Washington St., BOSwOT. IMPORTERS AND SOLE AGENTS IN THE UNITED STATES FOR THE CELEBRATED Voigtl' huder &,o AND Darlot Lenses, For Portraits, Views and Stereo. Work. >ify ouf New ytefeogdopi Iherqe$e, if you WMavt the D3e$t ii Nik-et. SEND FOR PRICE LIST. Try the Bestl I? YOU WANT A GOOD FEIBOTYPE, USE THE DALLEEYER LENS Upon the ADAMANTEAIN PLATES, Manufactured by JOHI- DEAT & CO., WO0CESTER, MASS. E. U X. T. ANTHONY & CO., TRADE AGENTS, 591 BROADWAY, NEW YORE CITY. Edward Mead & Co., 304 N. FOURTH ST,, ST. LOUIS, 0o, Third Door from Olive, Next to Everett House. OLDEST STOCK DEPOT IN THE WEST. Keep a full Line of Photographers' Supplies, including best of Chemicals, Paper Goods, Albums, Glass, Frames and Backgrounds. Voigtlander's, Darlot's, the E. A. and Peerless Tubes of all Sizes. Anthony's Ether, Chemicals, Chairs and head Rests. Apparatus of all Makes. Catalogue will be sent to parties ordering ir:. Bevelled Edge Card Mounts-the latest Novelty. Albumen Paper, received fresh every week, of all the celebrated Foreign and American makes. MIIEADWS SPECIALTIES: I.X.L. Varnish, for Negs. I.X.L. Varnish, for Ambros. I.X.L. Positive Collodion. I I.X.L. Negative Collodion. These articles have received the most flattering endorsements from old experienced artists, and we can confidently recommend them as particularly adapted to our western climate, being made in and for this part of the world. Order anything you see on any Catalogue, and we can send it to you, as we keep a full line of everything that comes out, and sell as low as you can get it in the Eastern cities. JANUARY, x874. MAINE PHOTO. STOCK HOUSE! Tl'e aive,todk frouse of the 3a.t. - Everybody iSJVNew England and the Britis, EPryvinces East of 6/ostonz shozoud [ send to (Portland. AlZwcqys good Goods, q'zick dispatck anYd LOW prices. Pkhoiographdrs, Bumy of Hale, in (Portland. F62E~l'K F. HALE, JNo. 2 Free St. U11 of' inthony's floods canm be szpplied. David Tucker & Co., The Buffalo Photo, Warehouse. HEADQ UAR TERS,~ i_ I I)>'''M1 (I!3lI (IT liz Western Nezo York for Photographic Materials, Picture Frames, and Eve; ything Necessary for the Art, at the lowest figures. Buffalo, New York. MORRISON'S Wi e-Angle View Lenses. PATENTED MAY 21, 1872. m Wl These Lenses are absolutely rectilinear; they embrace an angle of >4 fully 100 degrees, and are the most rapid wieez-ngdre lenses made. We rec- U ommend them for use with the foregoing outfits. X PRICE OF MORRISON'S WIDE-ANGLE LENSES. L~~~~~~~~~~I)n~~~~~ Pi-ice. m Z No. 1, - diam. of lens, 4 x 4 in. plates, 3 in. equiv. focus, each, $25 00 oZ I/ No. 2, " " 4 xP5 " 3 " " " 5 00 n 4 No. 3, " " 4 x7 471 " 25 00 r No. 4, 1" " 5 x8 " 5~" " " 25 00 d0 __ z O Mliorrison's Rapid Stereoscopic Lenses L ~ f. FOR INSTANTANEOUS VIEWS OR LAWN GROUPS j β€” Are entirely different in many particulars from any other lenses in the 9O'm market. They are 6 inches focus and 1 inch in diameter, and of course q X can be obtained in matched pairs, if desired. By usinga set of diaphragms [ m provided they are adapted for making 5 x 8 views. C A novel and ingenious instantaneous drop is also provided, passing X through the brasswork, on the same principle as a central stop, by which t 2 absolutely instantaneous views, -4 x 5 inches, may be made, sharp all over to - the very edges, without being diaphragmed down. PRICE................. each, $40 00 "Peerless" Quick Acting Stereoscopic Lenses, FOR PORTRAITURE OR VIEWS. VWe-can':also furnish the following, either single or in pairs: The Lenses are especially designed for Stereoscopic Photography, and H Z are so constructed that they will work well for interiors or exteriors. D They are particularly adapted for- instantaneous work. Diameter of Lenses, 1- inch; focal length, 3& inches. - By removing the back lens and substituting the;-front combination, a focal length of 5. inches is obtained. C They are supplied with:six Waterhouse diaphragms in morocco case. U) Price, per pair...........25.................................... 00'I1 -Imitation Dallmeyer Lenses for Landscapes. Price, per pair......$17 00 SCOVILL'S PURE UHEMICALS AND ACCESSORIES,. F 0 MAEIING iE- IETE A GA.TIIVES. C 5 We offer with either N. P. U. Outfit "A," or A. O. Co. Outfits 3 201 and 202, the following goods packed securely in a woodcn >: case:- 2 4x5 Japanned Pans, I 1 lb. Alum, 1 4 oz. Grzaduate, 1 oz. Sulphuric Acid, 1 set 5 in. jap. Scales and Weights. 1 bottle Keystone Varnish, b wIM 1 oz. Bromide Ammonium, 1 doz. 4x5 " Dry Plates, - = 1 lb. Neutral Oxalate Potash, 1 Scovill Note Book, 1 " Proto Sulphate Iron, 1' Focusing Cloth, - 1 i " Hypo Sulphate Soda, 1 W. I. A. Ruby Lantern. m ~ PRICE, COMPLETE, $6.50.: w With N. P.U. Outfits " B" and "C," and A.O.Co. Outfit 203,we 0 supply the same goods with the exception of the substitution of O 5x 8 Pans and Plates for the 4x5 size., PRICE, COMPLETE, $7.50.' O Be sure that your chemicals are marked (D o S.P.C. 41- If they are thus labelled, success is guaranteed. > * Ready Sensitized Paper,... per dozen sheets, $3 00 c Scovill's Focusing Glasses,.... each, 75 COMPLETE EQUIPMENTS PROMPTLY FURNISHED. E. J. PULLMAN, 935 Pennsylvania Avenue, WASHISNGTON, D. C. American bptieal Company's Apparatus Outfits. This apparatus is manufactured in New York City under our immediate personal supervision; and, as we employ only highly skilled worko men, and use nothing but the choicest selected materials, we do not hesiS tate to assert that the products of our factory are unequaled in durability, excellence of workmanship, and style of finish. This fact is now freely e conceded not only in this country but throughout Great Britain, France, g. Germany, Australia, and South America. Quality being considered, our prices are moderate, as the same grade ti 9 of apparatus cannot be supplied fpr less-price. OUTFIT No. 201, complete, price $26 50, 9'' CONSISTS OF X, A MAHOGANY POLISHED CAMERA for taking pictures 4 x 4 inches, with CD: Foldino' Be/llows B'odiv, single swing, hinged bed, and brass guides. It has -o a shifting front for adjusting the sky and foreground, also~r -1 Patent Double Dry Plate Holder. 1 Taylor Folding Tripod. o 1 Canvas Case to contain Camera and Holder. - Id OUTFIT No. 202, complete, price $27 00, CONSISTS OF -) A FOLDING MAHOGANY CAMERA for taking 4 x 5 pictures, same style as O 201 Camera, also44 1 Patent Double Dry Plate Holder. 1 Canvas Carrying Case. ""r 1 Taylor Folding Tripod. e+ OUTFIT No. 203, complete, price $41.00,.~ CONSISTS OF A FOLDING MAHOGANY CAMERA, fully described in the American Optical W Company's Catalogue, and well known as the'76 Camera(see illustration.).It is adapted for taking 5 x 8 pictures, and also for stereoscopic viewstogether with 1 Patent Double Dry Plate Holder. 1 Canvas Catalogue, ndwell known as the 76 Camera see illustration.) 1 Taylor FoldingTripodlate older Cameras in Outfits 202 and 203 have shifting fronts, and are equal in - style and finish to the best of the American Optical Company's make. Our New PATENTED Double Dry Plate Holders are the best made, and answer the demand in dry plate work for something that will exclude all light. Prices of EXTRA Patent doutble DTy Plate Holders are as follows: 4 x 4 Holders for two Plates............each,$3 00 4x 5 ".......... 3 00 5 x 8 ""............. " 4 00 SCOVILL Port able0 DRY pLATE OUTFITS FO01R ANA.tTEURS. Old Style Equipment. ew Style Equipment. The increasing interest in Dry Plate Photography, and the impetus given by it to the work of the amateur, has created a demand for a special apparatus which is light, compact, and easily carried about. We are, as usual, up to the requirements of the times. The Cameras and Apparatus of our make are known to be in every respect the most accurate and of the lightest weight of any in the world. We beg to call your attention to the following Price Lists of NE PLUS ULTRA APPARATUS OUTFITS, All Articles of which are Warranted Accurate in every Respect. OUTFIT A, complete, price $10 00, comprises A VIEW CAMERA (black) with rubber bellows and rigid platform, for making 4 x 5 inch pictures. 1 Patent Patent Double Dry Plate Holder. I Tripod Camera Stand. 1 "Waterbury" Achromatic Nickel Plated Lens with Standard English Flange. 1 Carrying Case. OUTFIT B, complete, price $12 00, comprises A VIEW CAMERA for taking 5 x 8 inch pictures. Same style as A Camera. 1 Patent Double Dry Plate Holder. 1 Tripod Camera Stand. 1 "Waterbury" Achromatic Nickel Plated Lens with Standard English Flange. 1 Carrying Case. OUTFIT C, complete, price $18 50, comprises A VIEW CAMERA (black) for making 5 x 8 inch pictures. This Camera is constructed so as to make either a Cabinet Picture on the full size of the plate (5 x 8 inches), or by substituting the extra front. (supplied with the outfit) and using the pair of lenses of shorter focus, it is admirably adapted for taking stereoscopic negatives, also by the same arrangement two small pictures, 4 x 5 inches each, of dissimilar objects can be made on the one plate. Included in-this outfit are also1 Patent Double Dry Plate Holder. 1 Large "Waterbury" Achromatic Nickel Plated Lens with Standard English Flange. 1 Pair "Waterbury" Achromatic Nickel Plated Matched Stereoscopic Lenses. 1 Tripod Camera Stand 1 Carrying Case. E. & H. T. ANTHONY & CO., Photographic Materials & Chromos, i91 Broadway, NEW YORK. MANUFACTURERS OF Photographic Varnishes, Collodion, Cottons, Bromides and Iodides, Cameo Presses, S. V. Passe Partouts, Cases, Posing Chairs, Curtains, and many other Gobds. Dealers in Everything Publishers of Stereo. that can contribute to Views, the Silver Sunsuccessful and conven- beam, and Anthony's ient photographic ma- Photographic Bulletin. nipulation. Se-ad for a copy. IMPORTERS OF Swiss Pink and Dresden Albumen, and Plain Saxe and Rives Papers, Porcelain Wrare, Evaporating Dishes, Genuine B.JT.C. Glass, Gold Saucers, Filtering?aaper. Also, Pyrogallic Acid, Hypo., German Glass Baths, Chromos, Large Plain and Colored Photographs, Stereoscopic Views, etc., etc. AGENTS FOR The Eureka Plates, Dean's Adamantean Ferro Plates, The Dallmeyer Lenses, Success Cameras, Woodward's Improved Solars, Bendann's Backgrounds, Etc., Etc., Etc. John R. Clemons, IMPORTER OF PHOTOGRAPHIC SAXE AND RIVES AND MANUFACTURER OF ALBUMEN AND ARROWROOT SALTED PAPERS. PINK and BLUE ALBUMEN PAPER constantly on Hand, or Made to Order, Clemons' New A.lbumen Paper, A superior article) introduced into the market about a year ago. It is equal, if noit superior to any Paper imported; the great demand proves slnch to be the case. It is praised by all who use it as to its keepin hite during warm weather; also, for its brilliancy and toningSqualities, and it is made in White, Pink, and Blue. - Sizes, mc~dium, 26 x 40 and 35 x 46. Clemons' Arrovyroot Salted Paper Has- stood the teit above all other makes for the last nine years. An article exteinsively used for all Plain, Solar, and Colored Work. Sizes,:,/ x 23, 26 x 40, and 35 x 46. Prices Lowever /tan any Foreign Make. Clemons' N. P. A. Varnish, For Plain Work and Retouching upon. Clemons' Golden Varnish, For Intensifying and Retouching upon. JOHN R, CLEMONS, Manufacturer, 915 Sansom St., FPHILI -AD1EELPHIA. eyip ie 0 foif L11 E. & H.T. A & Co,, FOITR I-STATE'' "'TITED STATES,