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The Camera in Sound Pictures — Howell and Duhray 145
The amount of noise produced in intermittent movements by the rapping of the film-feeding fingers against a stationary film, is determined by the amount of ''play" between finger and perforation.
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a ACCE.LERAT\ON BY A CONSTANT FORCE (GRAVITY) b •• •• OBTAINtD BY THE MOVEMENT
Figure 7. Comparative curves of the acceleration by a constant force with the acceleration obtained through the movement.
In the. movement here presented, the film-feeding fingers are .008" narrower than the film perforation, which condition limits the overthrow to .004", that is to say, the film-feeding fingers move along a path only .004" long before touching the faces of the perforation.
The extent of displacement is so small that the downward movement of the fingers is extremely slow at this moment, so that they may practically be considered as stationary at the instant in which they actually come into contact with the film perforation.
To insure a still greater resistance to wear, the ends of the film-feeding fingers are chromium plated.
In Figure 8 are shown five schematic drawings of the mechanism, at five different phases of movement.
It is well to remark that the schematic condition of the drawings does not permit illustrating the extremely small overthrow previously referred to.
In position 1, the film-feeding fingers are withdrawn from the perforations and the registration fingers are holding the film stationary by spring pressure. [Note: Experiments are being conducted to eliminate the use of springs] .
In position 2, the film-feeding fingers are shown during their upward motion. The film is still held in position by the registration