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THE REDUCTION PRINTING PROCESS 287
apertures decrease in the order given. The dimensions quoted previously refer to the camera apertures.
Reduction Picture Printing
The present work is mainly concerned with the production of 16-mm films of a technical quality as nearly as possible equal to those produced with 35-mm equipment. Because of this it is most convenient to consider firstly that process which is most widely used to produce high quality results at the moment and, as we have seen, such a process is known as Reduction Printing.
Before considering the actual equipment it will be as well to establish the optimum conditions which must be maintained throughout the process. The picture quality and, particularly, the mechanical steadiness, which is acceptable with 'home' projection, leaves much to be desired when magnified to the greater screen sizes employed when 16-mm films are used for purposes similar to and, to some extent, in competition with 35-mm pictures. Picture unsteadiness is, of course, most noticeable to observers following, for example, the operation of intricate mechanisms, outline drawings and the many types of diagram films used for visual education.
It would seem likely that, with the addition of sound to 16-mm films and the improvements made in Laboratory technique, the opinion gradually developed that 16-mm films should be capable of screen quality equal to that obtained with 35-mm films under comparable conditions. Whilst it is agreed that the existing average screen quality should be greatly improved, it can be readily proved that, even by applying to the entire 16-mm process working tolerances as close as those used with 35-mm films and equipment, it is fundamentally impossible to obtain absolute equality between both systems. The following comparison will indicate the magnitude of variation in screen picture position which may be tolerated in each case and, although such a comparison only deals with one specific problem that of picture unsteadiness it is also representative of the differences which may be expected when other aspects of the two film sizes are compared.
Firstly, it is necessary to establish the magnitude of screen picture unsteadiness which may be tolerated when 35-mm films are projected. Since it is not convenient to measure the percentage of actual picture movement at the screen surface, tolerances are always placed upon the motion between successive pictures or frames at the projection aperture. The following tolerances have been recommended by Messrs. Tuttle and Reid in a paper to the