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PRINCIPLES OF CINEMATOGRAPHY
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Fig. 133. — Principle of pilot-pin registration.
movement through the gate is retarded from maximum to minimum speed and, particularly, the velocity of movement still remaining after the intermittent mechanism has disengated from the film, (2) The coefficient of friction between the film and the channels of the gate through which it is moving. (3) The tension which exists between the film gate channels and which is intended to arrest the film after the claw has disengaged and also to maintain the film in a stationary position during the exposing period. (4) The effect which may be introduced by any system used to guide the film through the gate channels by a spring tension applied to the film edges.
Figure 133 indicates the principle of pilot pin registration and the sequence of operations performed by this unit in conjunction with a simple link claw. In diagram 'A' the claw has reached a point approximately mid-way between the start and end of the 'pull-down' stroke and, therefore, the film is moving through the gate at maximum velocity. The pilot pins *D' are therefore drawn away from the film. These pilot pins are attached to an accurately ground shaft, free to move horizontally within two bearings 'E'. A central portion of this shaft carries a cam follower, or yoke, *F\ which is machined to be a very close fit around cam 'G\ Cam 'G' is so designed that it will cause the pilot pins 'D' first to disengage from the film perforations and move to the right, then to remain motionless for a period equal to the duration of the exposure. The pilot pins then travel to the left, enter the film