Focus detecting device

Details Focus detecting device Focus detecting device

1975-11-06

1977-08-30

Hix, L. T.

Radiant energy

Ionic separation or analysis

Static field-type ion path-bending selecting means

250201, 250204, 352140, 354 60E, G02B 2302

Patent

active

040458040

ABSTRACT:
A focusing device for providing an indication of the in-focus condition of a lens relative to a scene and a focal plane, F.sub.0. An a.c. bridge circuit includes photoelectric elements in two legs thereof; the elements being physically positioned just in front and just behind, respectively, of focal planes F.sub.1, F.sub.2 which are optically at the same distance from the lens as focal plane F.sub.0. An a.c. input voltage is applied to the bridge, and the output therefrom is an a.c. voltage which has a phase and an amplitude dependent upon the differential amount of light impinging on the first and second photoelectric elements. As the focal plane of the lens moves from a plane in front of F.sub.0 to a plane behind F.sub.0, the a.c. amplitude goes from maximum at phase 0.degree. to minimum at phase 180.degree., passing through zero amplitude when the lens is positioned to cause the light from the scene to be focused exactly at F.sub.0.

REFERENCES:
patent: RE27817 (1973-11-01), Craig
patent: 3529528 (1970-09-01), Leitz
patent: 3857031 (1974-12-01), Sinclair et al.
patent: 3883689 (1975-05-01), Mansour et al.
patent: 3946222 (1976-03-01), Swanberg

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