Unidirectional focussing system

Details Unidirectional focussing system Unidirectional focussing system

1979-06-26

1981-12-01

Hix, L. T.

Optics: motion pictures

Removable film strip magazine type

354 31, 352140, G03B 310

Patent

active

043033199

ABSTRACT:
At the start of each focussing operation, the camera objective is at a first extreme subject-distance setting and is moved in a first direction therefrom towards the second extreme subject-distance setting. A focus-evaluating circuit comprises first and second photodetectors located to receive light from the subject and a comparing circuit which compares the light incident on the photodetectors and in dependence upon the present subject-distance setting generates first and second signals respectively indicating that the subject-distance setting should be changed in the first direction or in the opposite second direction, such circuit having bidirectional character and furthermore establishing a tolerance range of acceptable distance-setting error within which both the first and second signals are generated. During the unidirectional change of subject-distance setting, the appearance of the first signal leads to generation of a stop signal commanding that the progressive change of distance setting be stopped. Accordingly, the unidirectional change of setting is commanded to stop at the point where the changing distance setting just enters into the tolerance range of the bidirectional evaluating circuitry.

REFERENCES:
patent: 3274914 (1966-09-01), Biedermann et al.
patent: 3617128 (1971-11-01), Harvey
patent: 3906389 (1975-09-01), Matsumoto et al.
patent: 4053240 (1977-11-01), Aizawa et al.
patent: 4091275 (1978-05-01), Wilwerding

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