Film Pulldown Claw

Film Pull-Down Claw

 

for movie cameras and projectors

 

 

      This is a concept in 1977 by Steve Hines for a quiet film pull-down claw.  The claw bounces vertically and horizontally at different rates to create a gentle start and stop, while providing the maximum speed during the film advance.   This quiet pull-down technique is well suited for available-light sound movie cameras.  

Lab notebook entry.	Parallel spring-steel arms provide flexibility for vertical and horizontal motion without noisy sliding parts.

 

The film pull-down claw moves in a Lissajous pattern, created by the phase relationship of vibrating vertical and horizontal spring-steel parallelogram supports.

 

 

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Duty Cycle

    The quicker the film pulldown, the more time there is available for exposure.  

     In the 2:1-ratio version the pulldown occupies approximately 25% of the total path, requiring a 90° rotating dark shutter, therefore allowing for a 270° open shutter, for longer exposure than the typical 180° shutter-angle camera.  

2:1 ratio	3:1 ratio	4:1 ratio
36Hz vertical    18Hz horiz.	54Hz vertical    18Hz horiz.	72Hz vertical      18Hz horiz.
≈270° open shutter	≈300° open shutter	≈315° open shutter

 

 

 

 

      All patterns are based on the 18 Hz frame rate of Super 8 cameras.  Other ratio Lissajous patterns can be tried to increase shutter exposure even further, with increasing risk of tearing the film.  

 

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Hines’ Kodak Lab Notebook entry, March 9, 1977

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      Further development would include adding electromagnetic coils to keep the mechanism in motion.

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For consulting, please contact Steve Hines at: