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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1289, May 18, 1883
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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- Titel
- The photographic news
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May 18, 1883.] THE PHOTOGRAPHIC NEWS. is obtained, but at a considerable sacrifice in the definition and has no fine adjustment. Indeed, that is not necessary with ah ordinary camera focussing-screen is too coarsely ground, and powers less than a half-inch object glass. You will see that the should be substituted by something very much finer. Various eye-piece is taken out ; with the eye-piece a much larger image substitutes have been proposed for ground glass. I find that microscope knows, drowns out the details of an object. These remarks are, of course, not applicable to the higher powers of the microscope, where the lenses are so small that it is absolutely necessary to employ the strongest possible light. The object to be photographed should be carefully and cleanly mounted. Every particle of dirt in the preparation is, of course, magnified as well as the object, and clean slides should always be chosen. The object should be as transparent as possible, and have no colour impervious to light. A great many preparations in Canada balsam are of a deep brown colour, and, of course, when these are photographed, nothing but an outline of the object is obtained. course, all defects in the manipulation may be remedied, but the utmost care is requisite to produce good work. The much loss of light, the light having other four surfaces in the eye-piece to pass through. The object glass in the microscope on the table is a two-inch by Mr. Wray, and you can see the object on the camera focussing screen has an abundance of light, and would allow a quick exposure. The lamp is placed a little to the left hand side of the mirror of the microscope, and the light is thrown upon the object by inclining the mirror. With such an object glass as a two-inch of this kind no condenser or any other apparatus is required. The mirror used is simply a flat piece of silver, and not particularly well polished, and yet there is plenty of light. The piece of silver was originally a florin. It is necessary to point out here that very much depends upon the way in which the object is lighted. In almost every published description I have seen of methods of taking micro photographs, one is told to use a large bull’s-eye condenser to make the rays parallel, and then another one is interposed to bring them to a focus on the object. Now I would ask, does any microscopist, when sitting quietly examining objects with his microscope, ever throw such a quantity of light on any object? Why, in every case we modify the light, and try to examine the object with as little of it as possible. The sensitive plate in the camera should be treated in the same way as we use our own eyes. Give the plate the necessary quantity of light, but no more. Too much light, every one who can use a Some operators use a very long camera, so as to obtain an image at once of the proper size for a transparency. By this means the intensity of the light on the sensitive plate is very much weakened, and the exposure required much longer. I prefer a short camera and a smaller image, which is better lighted and requires a shorter exposure. This is no drawback, because if one gets a good negative, the necessary size for a transparency can be readily got when copying. I need not enter upon the kind of sensitive film to be employed. That is a matter of taste and convenience. great many object glasses they are coincident, or nearly so. When they are not coincident, they may be made so by fitting in behind the object glass an ordinary spectacle lens of from 5 to 10 inches focus. Experiment only can tell which is the correct one to use. But if it can be dispensed with, so much the better, as it intro duces another element for destroying the perfection of the image. The most particular care is necessary in order to get a sharp image on the focussing-screen. This is a more difficult matter than is generally supposed, and the evidence of this is the extreme rarity of very good photographs of microscope objects. One hardly ever sees a good micro-photograph, at least one which satisfies the eye of a trained microscopist. Whatever be the cause, whether there has been a want of attention in the sharp focussing, a want of correct register in the camera, a want of coincidence in the visual and actinic foci of the objective employed, or an error in lighting the object, micro-photographs, as a rule, are not good. Some give nothing but outline and a black patch. Take, for instance, photographs of parasites ; some give a little detail, but only hint at the beauty which lies in the object, such as photographs of the proboscis of the blow-fly ; others, such as photos of the coarser striated diatomaceg, certainly give the details pretty well, but when minutely examined it is seen that there is a great want of sharpness. Of the best I can get is an ordinary quarter-plate covered with a very thin film of wax. Micro-photography has always been the hobby of a select few. Microscopes are plentiful nowadays, but photography and micro scopy do not seem to take kindly to each other, else we should have very much more about it in the literature of these subjects. It requires great and lengthened experience to become an ac complished microscopist, but the photographic art is much more easily acquired. I have shown you that simple apparatus, if good, may produce excellent results with the lower powers. The higher powers of the microscope when used in photography re quire special apparatus which none of the members of this Society, so far as I know, possess. With very high powers a heliostat is necessary. Colonel Dr. Woodward, of the United States Medical Museum, has produced accurate and fine photo graphs of Amphipleura pellucida, showing the striation, the lines on which are only the 100,000 of an inch apart. These are feats of manipulation, however, which none of us can expect to rival. But they should make us do our very best with the apparatus we have got, and it will be a great end gained, if, after what you have heard and seen to-night, however imperfectly performed our efforts have been, a number of the members of this Society who have microscopes, and are skilled in photography, should take kindly to the subject, and be able to show at our meetings in the beginning of next session a plentiful supply of good lan- : tern transparencies of microscopic objects, so as to enable the Society to devote a special evening to their exhibition. scope is fixed to the board in front of the camera, and with the eye-piece taken out the tube is put about an inch inside the camera, in the hole into which the camera lens is usually screwed. The tube of the microscope requires to have placed inside it either a diaphragm at the end next the camera, to cut off any false light which would be reflected from the side of the tube, or, what serves the purpose equally well, a piece of stiff paper blackened with lampblack and lacquer, wrapped round like a tube and pushed into the tube of the microscope, such as I show you now. The microscope may be a very simple one if only low powers are used, but it is essential that it should be made to incline. It is also necessary, if good results are to be expected, that the very best lenses should be used. You will notice that the one on the table is a very simple instrument, but very steady. It has been properly prepared, and the apparatus all in order, the mere taking of the photograph is as easy and simple as taking that of any other negative . The difficulty—what there is of difficulty—consists in the proper arrangement of 1 the apparatus, the selection of a carefully mounted object, the proper arrange ment of the light, the selection of the proper objective to be used, and, what is of more consequence perhaps than all the rest, obtaining a sharp and fine focus upon the screen of the camera. It will be well to go over these details as they are mentioned above, and when they have been considered seriatim, followed by the practical exhibition of the apparatus and the taking of a negative, there cannot be much difficulty in understanding what is necessary to be done and how to do it. The best way to proceed is to get a straight flat pine board about the width of the camera to be used, and at the one end of it to fix the camera at such a height that the tube of the micro scope to be employed, which is fixed at the other end, shall project into the front of the camera as near as may be opposite to the centre of the focussing-screen. This may be done, as you can see, on the board on the table by placing pieces of wood below the camera transverse to the length of the board, and fixing the camera firmly on these by a screw fr im beneath. Any camera will serve the purpose, either short or long. The micro The objective to be employed should with low powers be such as to include the whole of the object in the field. An object glass of about two inches solar focus is about the best for photo graphing sections of wood, whole insects, &c. Mr. Wray makes a very perfect single lens of that kind at the price of 17s. It is one of the very best I have seen. It has a wide aperture, and gives a great deal of light, with a very flat field. The apparatus with a lens of this kind is not expensive. Almost every object, however, requires one particular object glass to bring out its beauties, and although a single low power glsss may do very well to begin with, a larger number is required as you proceed to work upon finer objects, which require glasses of greater separating power. A good deal has been said and written as to object glasses requiting correction so as to make the chemical and visual foci coincide. I believe it will be found that in a
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