A CAMERA for PHOTOGRAPHIC DEMONSTRATION DAVID H. GURINSKY Washington Square College of A r t s and Sciences. X e w York University, New
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A CAMEKAPOR CLASSROOMDEMUNSTRATIOK UF
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Pnoroo~nvnrcPROCESS
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OST demonstrations of photography deal primarily with the characteristics of the sensitive emulsion and fail to illustrate the taking of the picture and the subsequent treatme& of the a m . Although the taking of the picture itself does not present any difficulty, the development and fixing of the film require special conditions and more time than is usually available in the classroom. To obviate these difficulties, a camera has been constructed in which exposure, development, and fixing can be performed without the removal of the film. These operations are made to yield a direct positive image on "tintype" paper' which consists of a sensitive emulsion on a jet-black surface. The portions struck by light are converted to silver on developing, while the unaffected silver halide is dissolved by hypo in the usual way. The silver deposit reflects more light than the black surface on which it lies, thus giving the impression of a positive. The camera is made of sheet iron covered with glyptalz inside and out to prevent corrosion. Since The paper is obtainable from the Benson Dry Plate and Camera Company, 166 Bowery, New York City. ' Obtainable through the General Electric Company.
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it was desired to make use of Yllx X 58/g" tintype paper, the camera width and height were fixed by this choice. These dimensions are: height 5518", width 3/,". The length of the camera, i. e., the distance from lens to tintype, is determined by the focal length of the lens. In our case this was ?14". TOlend rigidity to the box proper a collar '/g" X 5/g" is soldered around the top. The camera is made light- and liquid-tight by means of a rubber ., casket fitted into the cover. The latter is fastened to the box by four wing bolts as shown in the photograph. The holder for the film consists of two strips of metal, acting as guides, soldered to the walls of the box about 1 mm. removed from the back. Near the front of the camera, a piece of copper tubing, bent in the form of a snake so as to allow the passage of liquid but not light, is soldered to a threaded cup into which a plug with a milled head screws. The complete experiment is carried out as follows. The camera is loaded in the darkroom. If two No. 2 Photoflood lamps, four feet away from the subject to he photomaphed, and an f/7?lens are used, the exposke is-30ieconds. SU& an exposure requires that the camera be rested on some firm object such as a stool while taking the picture. The milled cap is then unscrewed and 100 cc. of developing-fixing solution are introduced with the aid of a funnel. (forsimvltaneovn developina and fiiinc with the same ~ I u t i 0 0 ) (6 minutes a t lS°C.) 13.3 mams hvdraauinone . . 49.5 ;rams sodium rulfite 35.5 nrams sodium carbonate 106.0
grams hypo
4 6 . 0 ce. concentrated ammooium hydroxide diluted t o 600 ce.
During this operation, the camera is tilted forward so that the solution will not come in contact with the tintype until all of it has been introduced. The cap is now replaced and the film is developed and fixed by moving the solution back and forth over it for five minutes. While this is going on, the demonstrator has ample time to explain what is happening in the enclosed box. Finally, the wing bolts are removed, the tintype is drawn out and rinsed under the tap. The picture is now ready to show to the class. If it is desired to cut down exposure time, it is sugnested that the tintvues be sensitized in one of the following ways: (1)..exposure to mercury vapor for 24 hours, (2) very short exposure to a feeble light, (3) treatment with ammonia water.
Because of the widespread interest in photography and the novelty of the experiment and also because a member or members of the class may participate in it, the above procedure is keenly followed by the students and we believe it succeeds like no other in putting
across the elementary principles of the photographic process. I wish to express my thanks to Dr. William F. Ehret whose suggestions and coijperation made this experiment possible.
