Automatic focusing system for projectors

Details Automatic focusing system for projectors Automatic focusing system for projectors

1978-04-19

1980-04-15

Stephan, Steven L.

Optics: image projectors

Selective projection on distant or cabinet screen

353101, G03B 2122

Patent

active

041981383

ABSTRACT:
The present invention provides a system for automatically focusing a projected film image by maintaining a predetermined distance along the optical axis between the emulsion on the surface of the film and the projection lens. The system includes a movable carriage for mounting the projection lens and an electro-optic sensor mounted for movement with the carriage for maintaining the predetermined distance. The electro-optic scanner includes a light source and lens assembly for focusing a beam of light onto the surface of the film and a lens for focusing the reflected image onto a dual phototransistor receptor. A servo-amplifier is connected to the output of the dual phototransistor to provide appropriate signals to the carriage drive mechanism to maintain said predetermined distance. The servo-amplifier utilizes both positional and rate feedback to provide faster operation and settling. The inclusive angle between the light source and the photodetector is substantially reduced providing for a more compact and reliable system.

REFERENCES:
patent: 3249006 (1966-05-01), Stauffer
patent: 3517992 (1970-06-01), Holle
patent: 3628863 (1971-12-01), Kottler et al.
patent: 4030821 (1977-06-01), Badalich

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