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blade of the occulting shutter opens to let light pass through the film.
The eccentric-star intermittent no doubt has a few disadvantages, such as necessity of operating the machine in only one direction of rotation at all times. Another disadvantage of the eccentric star is the proximity of the slots to the curved edges of the star. This defect can be corrected with a larger, flanged star, and amounts to little more than a matter of experimental work.
The writer feels that the eccentric-star intermittent movement is far superior to any other intermit
tent mechanism of the geneva type in approaching the optimum 60degree pulldown. An outstanding advantage of the 60-degree pulldown is that it makes possible the use of a 3-blade shutter with 60degree openings to give a 72-cycle cutoff frequency with 50 per cent light transmission.
Geneva movements for 16 mm. projectors are far superior to claw intermittents for many reasons. A particular advantage of geneva-type mechanisms is the placement of star and cam in an oil-filled housing for quiet operation and a long life of
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satisfactory service. Isolation of mechanical shocks generated in these mechanisms by large forces of acceleration may be accomplished by using two separate, but interlocked, synchronous motors, one for the intermittent and the other for the continuous film-drive and sound-head.
Useful data for the calculation of
FIG. 7. An eccentric-star intermittent with slanting, or non-radial, slots. The asymmetrical curve plots the velocity of this movement during pulldown.
these high-speed intermittent movements are scattered through a large mass of technical literature. Among the many articles that provide good examples of the problems encountered in this interesting field of motion picture engineering are "Mechanisms for Intermittent Motion" by Otto Lichtwitz in Machine Design (December 1951, January, February, and March 1952) ; "The Application of Pure Mathematics to the Solution of Geneva Ratios" by R. W. Jones, SMPTE Journal (July 1946) ; "Design Factors in 35-mm Intermittent Mechanisms" by Arthur Hayek, Journal of the SMPTE (November 1947), and 'Fast-Cycling Intermittent for 16-mm. Film" by Warren R. Isom, Journal of the SMPTE (January 1954).
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INTERNATIONAL PROJECTIONIST • NOVEMBER 1955