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Sept., 1945
8000 PICTURES PER SECOND
173
effort to guide the film at these high speeds and still prevent weaving and "breathing" at the image plane.
The film control in the Fastax cameras is very simple and yet highly efficient. The film path has been arranged so as to permit the sprocket holes to engage at least 10 pairs of sprocket teeth at all times as the film travels around the sprocket from A to C, Fig. 1. This secures the film firmly on the periphery of the sprocket as it passes the aperture at B, minimizing the effect of the centrifugal forces that would tend to throw the film out of the image plane and cause the pictures to go in and out of focus, or "breathe."
The sprocket is coupled directly to the driving motor and is used to propel the film through the camera by its 2 rows of specially designed
FILM
-\
r->
/ — ^
B
SPROCKET FIG. 2.
and accurately cut teeth. The lateral weave of the film is practically eliminated by having the width of one row of teeth (A) on the sprocket almost the width of the film perforations, Fig. 2. These features assure uniform travel of the film at the high speeds of operation involved, but the means used make it necessary for the camera to employ accurately perforated film that is within 0.5 per cent of full pitch.
In addition to smooth film movement at high speed, it is necessary to provide suitable optical compensation to allow the image to follow the movement of the film during the exposure period for each frame.
There are several methods of optical compensation that have been used by designers in the past. One method is the use of a series of matched lenses2 3 4 of high aperture located around the periphery of a large wheel which rotates in front of the film. The lens wheel is driven at a rate of speed equal to the film as it passes the picture aperture. In this manner, one exposure is made through each lens as