Optics: motion pictures – Optical rectifier type – Reflector angularly displaced about fixed axis
Patent
1974-02-11
1977-01-18
Hayes, Monroe H.
Optics: motion pictures
Optical rectifier type
Reflector angularly displaced about fixed axis
G03B 4110
Patent
active
040036456
ABSTRACT:
A film strip is continuously advanced past a film gate of a camera or a projector while light coming from the strip through the film gate is reflected by a pivotable mirror keeping a beam of light trained upon a specific area of the strip, i.e., a frame, during a major part of a recurrent operating cycle. The mirror is reciprocated during each operating cycle under the control of an electrical signal generator synchronized with the strip-feeding mechanism, either directly or through markings (e.g., perforations) on the film strip, and performs a relatively slow forward sweep followed by a relatively fast return sweep, the latter being effected by a pulse of one polarity immediately followed by a pulse of opposite polarity arresting the mirror drive. In one embodiment (FIG. 8), the control circuit for the mirror drive includes a differential amplifier responsive to a balanced pickup of light from a marginal film perforation, serving as a synchronizing mark, by two photocells illuminated by some of the light rays reflected by the mirror, the disappearance of the mark behind the film gate resulting in the generation of the sweep-reversing pulse pair. In another embodiment (FIG. 15), the image of a film perforation traverses a vignetting mask of triangular shape and impinges on a transducer which converts the light rays passed by the mask into a sawtooth voltage for the forward sweep, the attainment of a predetermined voltage threshold triggering the generation of the pulse pair. In a further embodiment (FIG. 20), the forward sweep is stabilized by an error signal fed back to the control circuit from a differential amplifier receiving a reference voltage and the output of a photodiode illuminated by part of the light from a film frame to be projected onto a receiving screen, the photodiode output remaining constant during the forward sweep with synchronous motion. Synchronization may also be carried out (FIG. 16) with the aid of a swingable claw engaging in successive perforations of the advancing film strip.
REFERENCES:
patent: 2843006 (1958-07-01), Tyler
patent: 3067284 (1962-12-01), Baldwin
patent: 3677626 (1972-07-01), Ferrari
Broeckl Heinz
Forch Friedrich
Freudenschuss Otto
Keznickl Eduard
Patels Gottfried
Dubno Herbert
Hauser Raimund
Hayes Monroe H.
Montague Ernest G.
Ross Karl F.
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