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THE REDUCTION PRINTING PROCESS 303
between pins T and '5* is shortened to the minimum length permitted will still pass successfully through the machine. Similarly, as seen at the left of Figure 135, any film in which the overall pitch between pins T and '5' is increased to the maximum length permitted, will also pass successfully through the machine. However, it must be pointed out that, for other reasons not relevant to the present considerations, it does not necessarily follow that all such films will be free from picture unsteadiness when viewed on the screen. The maintenance of pilot pin, claw pin and film pitch dimensions to be within the accepted tolerances ensures that the film will pass through the machine without causing any damage to the edges of the perforations.
Printer Adjustments
Turning now to consider refinements which may be provided with any reduction printing equipment, we find that five main requirements are usually fulfilled: (1) means to adjust the framing of the 35-mm negative film, (2) provision to adjust the intensity of the exposure, (3) interchangeable aperture plates to mask either sound or silent 35-mm picture areas, (4) provision to adjust the reduction ratios and, (5) provision to adjust the sharpness of the 16-mm image. Although some printers do not provide all the foregoing refinements, it is usual to find the first two 35-mm film framing and exposure regulation, fitted to every machine.
The accuracy with which the boundary of the 35-mm picture is located with respect to the perforations depends upon the distance between the intermittent mechanism and the aperture in the original camera used to produce the negative. An appreciable variation in this dimension has been known to exist between cameras of different types and, unless some correction is available in the reduction printer, the top of the picture may be lost and a black border, larger than that required, may be printed at the bottom of the 16-mm picture area. If the bottom of the 35-mm picture is lost then the width of the black border is increased at the top of the 16-mm picture area. Obviously, some means must be provided to correctly align the picture area and the aperture in the printer and, in early machines, this was accomplished by moving the aperture plate in a vertical direction, as shown in Diagram 'A', Figure 136. This system of correction is not satisfactory since it must cause the 16-mm image to be misplaced with respect to the perforations in that film.
Firstly, let us assume that, in the perfect case, the 35-mm claw in the printer will bring the film t® rest so that picture 'A' is
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