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COMPOSITE OF A8, B
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TEST PATTERN B PRINT OF COMPOSITE
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Fig. 3. Target patterns.
tern of using double-exposed images to indicate out-of-register, which is familiar to some, was selected not only to enable convenient viewing by projection but also to permit the use of a single-channel recording device.
Two "targets," illustrated in Fig. 3, were provided in order that exposure, first to one and then to the other, would result in cross-line patterns and also form "light slits," the sizes of which vary depending on the differences in positioning of the film during the first and second exposure. The crossover lines, forming tapered wedges, are used primarily for visual studies of the projected image, whereas the stepped slits are arranged conveniently for photoelectric recording of the vertical and horizontal variations. Figure 4 represents the composite formed by superimposing image of target A and target B, shown in Fig. 3. The size of the original target was selected so as to give successive step distances of 0.002 in.
Fig. 4. Composite of target patterns.
on the wedge image formed on the camera film. This provided a means of visual checking of the approximate variations in "slit" width on the printed film during projection. The system of superimposing images described is applicable not only to testing registration ability of equipment for a particular film, but valuable, as in this case, in evaluating different films or types of perforation holes on given equipment. In the latter case, the same camera, printer and related apparatus were used for all comparison tests, thereby eliminating variables in equipment. It is well to point out that in testing for registration, by the method of superimposing films, the maximum shift of the first to second images may be twice that for either image separately. This total shift of one with respect to the other, however, is what may be encountered in actual picture making and consequently is indicative of the true situation.
W. G. Hill: Modified Negative Perforation
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