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PRINTING MOTION PICTURE FILM
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NEGATIVE
Fig. 65. — A rotary contact sound film printer.
the constant speed supply sprocket 'G', under the guide roller 'J', over a loop-size controlling roller 'K' and over the negative film at a point on the scanning drum *E\ The two films are held in contact by a spring loaded pressure roller 'L\ From this point the positive film passes in a free loop to the lower take-up sprocket 'M\
As is well known from the theory of belt drives and pulley wheels, the surfaces of a belt, when wrapped round a pulley, are not of the same length as those sections which are not in contact with the pulley. Referring now to Figure 65A, let us suppose that belt 'A' is wrapped round pulley *B\ The inner surface of the belt (at 'C) will be compressed, a neutral plane *D' will remain at the original length, whilst the outer surface 'E' will be stretched. If a second belt is now brought into contact with the first one, and caused to curve slightly in the same direction as the first belt, its inner surface 'G' will be compressed and the outer surface 'H' will be stretched.
It is generally agreed that a processed film is always shorter in pitch than unprocessed raw stock. If, therefore, we let the first belt 'A' Figure 65A, be the negative film 'A', as shown in Figure 65, and seen to be wrapped round the scanning drum *E', and let the outer surface 'E\ Figure 65A, be the emulsion surface of the negative film, we see that this negative emulsion surface will be stretched (it has just been stated that negative films are normally