Illuminating and indexing system for perforated cine film

摘要

The system indexes a film, perforated at one or both sides along the projection window. A rotary mask (71) covers the window during film movement and has a clear sector for projection indexing using a lug with a point travelling along a closed oblong curve. It engages with and frees the film at opposite ends of the path. The mechanism is driven by two shafts (30,20) rotating in the same direction. The first of these is coupled by a first crank to a first joint on the lug at the end furthest from the point and the second via a second crank, a joint and a link to a third joint at the middle of the lug. The second shaft (20) has an angular velocity n times that of the first, n is a whole number equal to or greater than 2. The clear sector of the masking disc (71) is adjustable in proportion to the angular velocity. The diameter of the disc can be adjustable in inverse proportion to this velocity, and its centre is moved towards the window as its diameter increases.