Journal of the Society of Motion Picture and Television Engineers (1950-1954)

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FREE ON SHAFT Fig. 5. Simplified mechanical schematic to illustrate use of epicyclic gears to permit changing the position of one film sprocket relative to the other. Browder in the design of this optical system. The various considerations of performance and manufacture indicate that the best compromise is a prism having 12 faces. Each face is active for a total rotation of the prism of 30° or plus and minus 15° from normal, plus the angle subtended by the objective-lens aperture. This aperture takes the form of a slit with its long dimension parallel to the axis of the prism to keep its subtended angle at a minimum, consistent with reasonable light conservation. However, due to this aperture effect, successive frames are projected as lap dissolves, the overlap being of short duration, representing the time required for the edge between two prism faces to pass across the effective width of the lens aperture. The prism is shown in Fig. 6 with the adjacent mirror D which turns the axis downward through the objective lens. This mirror is rotatable between stops to shift the image for viewing the sound track. The shift lever is shown as E. Synchronization Control Differential synchronization between the sound and picture films is accomplished by a series of gears on the jack shafts in the sound and picture film drives. With the two shafts interlocked, synchronization may be changed by indicated amounts while the machine is in operation or at standstill. Figure 5 is a simplified mechanical schematic of the differential synchronizer. A represents the sound jack shaft on which a gear B is mounted ; G represents the picture jack shaft on which a gear D is mounted. The gears B and D are coupled through an integral pair of epicyclic gears E, the shaft of which is mounted on the carrier F. This assembly floats on the jack shaft and may be rotated about it by the Crane, Hauser and Manley: Westrex Film Editer 321