Film Pulldown Claw

Movie-Film Pulldown Claw

 

 

      This is a 1977 concept, by Steve Hines at the Kodak Research Laboratories, for a movie-camera pulldown claw, with none of the usual mechanical play of sliding or rotating parts that create chatter in typical cameras.  This quiet film-pulldown approach is well suited in available-light sound movie cameras.  

     Parallel spring-steel arms provide flexibility for vertical and horizontal motion of the pull-down claw to advance the film.  

 

 

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

      The claw starts pulling the film down with a gently increasing speed, and then slows to a stop at the bottom of the pulldown.

 


 

Duty Cycle

    The quicker the film pulldown, the longer time available for exposure.  

     The film pulldown is on the left side of the Lissajous pattern.  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.  

 


 

Hines’ Kodak Lab Notebook entry, March 9, 1977


 

      Further development would include redesign where the mechanism would wrap around the film cartridge (to leave room for the shutter and camera lens), and adding electromagnetic coils to keep the mechanism in motion.  As I write this in 2022, 45 years later, and with the near total adoption of digital video cameras, there would be no point in developing it further.


 

For consulting, please contact Steve Hines at:

HinesLab
USA
ph. 818-507-5812
email: Steve@HinesLab.com