Those who for years have had occasion to use a comparison microscope for the examination of bullets and other objects know how very tiring such examinations may become. Not only are they tiring, but they are productive of eyestrain.
Both of these difficulties disappear with the use of the comparison camera (1) * - the basic idea of which was suggested by May and by Lewis. The operator sits in a comfortable position looking directly ahead at images on a large ground-glass screen. The images are large and clear and are seen by both eyes and are viewed at a normal and comfortable distance, thus materially reducing eyestrain.
'Numbers in parentheses refer to Literature Citations given at the end of the chapter.
A series of knurled control knobs, placed in line a few inches below the ground glass, and one at either side of the ground glass enable the operator to move the specimens in any desired direction and rotate them. After all adjustments of the two juxtaposed images have been made, one sees on the ground glass exactly what he may expect to see in the finished photograph. A time switch enables him to expose the plate or film for a predetermined interval.
Both plates and cut films may be used. Eastman Panatomic-X film is very satisfactory because of its lack of grain and its sensitivity to all colors. A „glycin" developer is recommended because it gives very fine grain and the desired contrast.
The complete assembly is shown in Fig. 61. For the sake of clarity in description it is probably best to divide the instrument into several parts and describe each separately.
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