Photographic plate

“ If we take, for the sake of simplicity, not a picture, but a scale with four or five-tone gradations from light to deep black, the light tones will act more or less on the sensitive photographic plate according to their degree of brightness, but as the rays of light have to pass through the cross-lined screen interposed between the lens and sensitive plate, and as the rays can only pass through the transparent parts and not through the opaque, no homogeneous surface is obtained on the negative, but a tone produced by the cross-lines of the screen. ”

“ Let us imagine that the exposure has been made with an ordinary lens and camera, and that it is a landscape seeming to grow beneath the experimenter's eyes. At first only the most conspicuous objects make their appearance. But gradually the process extends, until finally every tiny detail is reproduced with marvellous fidelity to the original. The photographic plate, when developed in this way, is called a "negative." For in Nature luminous points, or sources of light, are bright, while the developing negative turns dark wherever light has acted. ”

“ Zinc plates are also employed as provisory supports instead of glass, opal or porcelain plates. The modus operandi is exactly the same.30 The plates should be well planed, free from scratches, etc., and well polished to obtain glossy pictures without one having recourse to a film of collodion. For matt pictures, i.e., without gloss whatever, the plate should be finely granulated, and when waxing a very light pressure should be exerted to remove the excess of wax, else it might be quite impossible to strip off the picture in transferring on paper. ”

“ Since the introduction of these extremely sensitive plates photography has proved of the greatest aid in scientific investigations. In astronomy clusters ot stars and nebulae have been photographed, which no eye can see, even in the most powerful telescopes, for the photographic plate can be exposed for hours to the image, the action of the feeble light accumulating in the sensitive film, whereas in the eye, if the light is too feeble at once to affect the retina, prolonged gazing is wholly without effect. ”

“ It would, it seems to us, be very easy with multiplying backs to get large numbers of a form on one plate, and then to reproduce them by cheap photo-mechanical means, and though we have never yet heard of photographic wall-papers, yet there is no reason why they should not be manufactured, if made artistically. ”

“ To begin with, the real photographer will use plates instead of films, as much better pictures usually are possible by their use. Dry plates come a dozen in a box, usually packed face to face—that is, with the film or sensitive sides facing. The plate-holder must be loaded in a dark room or dark closet, with absolutely no exposure to daylight or any artificial light whatever except a very faint light from a dark-room lantern, a combination of ruby and yellow glass or paper. We should always test our dark room and light by means of a plate before we trust them to actual working conditions. ”

“ In connection with what has already been considered in relation to the reproduction of drawings, it may be well to refer to the making of plates from photographs. The selection of a good photograph is of the first importance. It should be brilliant, and with all the contrast of light and shade and as much detail as possible, for something is always lost in both these respects in the process of reproduction. A good plate can be made from a good photograph, but cannot from a bad one. ”

“ Now I will answer this question before going any further, because it has a bearing on the subject before us—the making of a handy and cheap camera obscura, which cannot fail to be a source of amusement and pleasure, especially when the sun shines.
The reason why the object on the photographer’s ground-glass plate is seen upside down is easily explained. Light, as I need hardly remind older boys, proceeds in straight lines from any illuminated object. It is thus thrown upon the photographer’s plate. A glance at the accompanying diagram (Fig. 1) will suffice to show what I mean. ”

“ Thus in this camera are offered the daylight loading feature and all the other conveniences of films, together with the ground [Pg 17] glass focusing feature of the plate camera. And the ground glass may be used for focusing before each exposure just as well when using films as when using plates.
The camera is equipped with an accurate focusing scale, so that it may be focused by scale if desired. You do not have to use the ground glass. But when you want it, it is always there. A rack and pinion attachment is supplied for ease in focusing. ”

“ At the first glance, an inexperienced person sees no reflection on the ground glass, but the eye soon becomes practiced to perceiving the inverted image there. Substitute a plate holder for the ground glass, see that the cap is on the lens, pull the slide out of the holder, place it on the top of the camera, or in a convenient place. If everything is now in readiness, and the time for exposing the sensitive plate determined, uncap the lens, re-capping it at the end of the allotted time, and replacing the slide in the holder. ”

“ By the aid of photography it is easy to prepare a plate, transparent where the zones of odd order fall, and opaque where those of even order fall. Such a plate has the power of a condensing lens, and gives an illumination out of all proportion to what could be obtained without it. An even greater effect (fourfold) can be attained by providing that the stoppage of the light from the alternate zones is replaced by a phase-reversal without loss of amplitude. ”

“ When open landscapes are being taken, during summer time, medium rapid plates generally will be quick enough, but many opportunities, for pictorial work, arise under conditions of atmosphere and light, in which to obtain fully exposed negatives with a shutter, demands a plate of extreme sensitiveness, and if for no other reason than that they offer this opportunity of carrying a varied assortment of plates, many workers prefer dark slides, to any form of magazine. ”

“ He knows that the film camera is more convenient, that it will load and unload in daylight, and as the films are much lighter and occupy less space than dry plates, he knows that the film camera is especially desirable for use at vacation time, when traveling, and on other occasions where light weight and the greatest convenience are necessary. On the other hand, he knows that the plate camera offers the advantage of ground glass focusing between each exposure—a very desirable feature to many as it insures absolutely sharp focus and does away with the estimating of distances. ”

“ Every light spot in the camera-picture becomes dark on the sensitive coating of the glass-plate. But where the shadows or dark parts of the camera-picture fall, the sensitive coating is less darkened, or not at all, if the shadows are very deep, and so these shadows of the camera-picture become the lights of the glass-picture, as the lights become the shadows. Again, the picture is reversed, just as in every camera-obscura where the image is received on a screen direct from the lens. ”

“ The light used is their own, and its feebleness renders it necessary to make long exposures, the length increasing as we attempt to get images of fainter objects. The invention of the dry plate, by making it possible to give very long exposures caused a revolution in celestial photography. With the wet plate, exposures were limited to the few minutes during which the film would remain wet; but the dry plate can remain in the telescope for days, weeks or even years if necessary. On the approach of daylight, the cap is put on the camera, or the plate removed into the dark room ”

“ A simpler method of obtaining the same result is to have a pinhole in the bellows of the camera; a brightly illuminated object at the side and rather in front of the camera will then throw an image on the plate. A considerable exposure will be needed to give a fair extra; but this will present no difficulties, as the pinhole will be open all the time the plate is in position, and not merely during the few seconds that the lens is uncapped for the photograph of the sitter. ”

“ Where no attempt at pictorial work is intended, and the important matter is simply that the object being photographed should be in the centre of the plate, then it is only necessary that the finder should show as wide an angle of vision, or a little wider than the lens being employed inside the camera. ”

“ In support of this may be urged the fact that the interposition of glass prevents the making of dark pictures. But on the other hand it must be remembered that celluloid and sheet-gelatine, also air-tight substances, are able to store up light and to give it out again. It is well known among photographers that to allow sunlight to fall on the inside of a camera is apt to have a “fogging” effect on a plate that is exposed in the camera afterwards, though the greatest care be taken to keep all external light from the plate. ”

“ A rapid rectilinear lens used for landscape work on a half plate would be much too short in focus for giving good portraits on the same sized plate, for in order to get the figure large enough it is necessary to place the camera so near the sitter as to produce distortion. For portraits on a half plate a lens of at least nine inches focus should be used and for a whole plate not less than sixteen or eighteen inches, and longer if possible. ”

“ It will be easily seen that if the lens we use only just covers the plate, that when the front is raised, the lower corners will have no image exposed on them, and the higher the lens is carried, the more of the lower part of the picture will be cut off. ”

“ With the wet-collodion process, usually the method employed by large photomechanical printers, this method can be used because it is a simple matter to carefully examine the glass plate to be employed, but it will be obvious that with the ordinary dry plate all the imperfections of the glass, such as dirt, scratches, air-bubbles, etc., will be clearly reproduced in the image. ”

“ For this reason a quick plate with a moderate gradation is to be preferred—as being most generally useful—but it should be a plate which is absolutely free from fog, and it should also be of as fine a grain as possible, the size of which has something to do with development. This is still more true when a camera stand and hand exposures are made. With a slow plate with feebler intensities of light, which must be the case when the lens is stopped down to admit of hand exposures, the gradation becomes more steep than if a fairly bright light be employed. ”

“ As a matter of fact all things being taken into consideration the larger the plate up to 12 × 10 or 15 × 12 employed the more rapidly will the worker progress.
Large plates, especially in architectural work, tend to make the operator more careful and conscientious when out with the camera; and even more so when in the developing room. So much more can be done with a large plate than with a small one; the use of a large plate moreover checks the common failing so prevalent among amateurs of rushing work and recklessly using plates. ”

“ The exposure having been made in the camera or in the printing frame, place the plate in the developing tray and pour upon it sufficient of the developing solution, mixed as directed, to cover the plate at once, and keep it in motion from time to time. Develop until detail in the high lights is plainly visible. ”

“ As the image is upside down, the blank corners will appear in the sky of the negative. It is then obvious that if the covering capacity of the lens is greater than needed for the plate used, the rising front may be used to a much greater extent than if you only use a lens advertised to cover the plate you are exposing. It must always be remembered that if the optical axis of the lens be raised above the centre of the plate the illumination may be unequal. ”

“ The dark slide must be light-tight, and made strong rather than for portability.
The lens should be rectilinear, and should be capable of covering the largest size plate the camera will take quite sharp to the corners. For a 12 by 10 plate a lens with an equivalent focus of about 18 inches will be best. ”

“ Fig. 60. centre of the board A. The camera, if of the box type, can be secured to the stand by means of a screw and wingnut, the screw being passed from the inside as shown. The beginner is advised to photograph only very bold and simple subjects, such as black and white drawings or enlargements. It is not safe to trust to the view-finders as to whether the whole of the picture is included on the plate, a piece of ground glass the same size as the plate sheaths, and used as a focussing screen, being much more reliable. ”

“ Formerly many photographers used a thin plate glass of very fine quality, but of late years the great demand for glass suitable for such purposes has made it possible for the manufacturers to prepare a cheaper quality, well adapted to the uses of photography. ”

“ A thin, narrow ribbon of pictures 40 feet in length is a vastly different thing to handle from a rigid glass plate. Its flexibility presented many perplexing obstacles which had to be overcome. Those who used the old roll film with the snap-shot hand-camera of the early days, can relate pathetic and humorous stories of the trials and tribulations they suffered in passing the awkward length of film through the developing and other baths. When it was unwound from the roller preparatory to immersion in the developing solution, it persisted in buckling and twisting into strange contortions. ”