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RE: Coments re: Film Reg.



>Steven Gladstone wrote:-

>A CLAW is used to engage the
>film, at or near the aperture plate, and pull the film through one frame at a
>time. Because the film starts and stops, there is a loop, above and below the
>aperture plate (GATE), between the gate where the film is moving in an
>intermittent motion, and  the sprocket rollers which drive the film. At least
>this is how my movie cameras, and my Regular 8mm, Super 8mm , and 16mm
>Projectors work.

Yes, but not 35mm projectors. As other answers have said, they use the
Geneva movement to drive a sprocket wheel intermittently. The film perfs
are always engaged in the sprocket teeth, so the film is pulled
intermittently through the gate.

To reduce flicker, the projector shutter is a 90 degree shutter, which
opens twice per frame - thus there are two 1/96th sec exposures of each
frame on the screen, with a 1/96th period of dark between each one.
Pull-down (the part of the cycle when the sprocket wheel is actually
moving) therefore has to happen in 1/96th of a second, in every
alternate dark period.  An intermittent telecine movement, which can use
digital delays, buffers and other black magic to provide the two fields
of each frame at the correct instant, may not be so constrained, and
there could be more gradual (1/48th sec) pull-down. Or something
entirely different!

BTW the loop in a 35mm projector is to isolate the intermittent image
gate movement from the absolutely continuous sound head transport.

~~~~~~~~~~~~~~~~~~~
            Dominic Case   
            Atlab Australia   
> ~~~~~~~~~~~~~~~~~~

+++ thanks to Rich Torpey of MTI/Image Group for support in 1997
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