Method and apparatus for detecting a focussing condition of an o

Details Method and apparatus for detecting a focussing condition of an o Method and apparatus for detecting a focussing condition of an o

1981-08-14

1984-06-19

Rosenberger, R. A.

Optics: measuring and testing

Lamp beam direction or pattern

With lamp focusing

250204, 369 45, G01J 136

Patent

active

044550855

ABSTRACT:
A method and apparatus for detecting a focussing error signal of an objective lens with respect to a video disc on which a light beam emitted from a laser light source is to be focussed as a light spot by the objective lens. A light flux reflected by the video disc is made incident upon a detection prism surface which is set substantially at a critical angle with respect to a central light ray in the reflected light flux, and two light fluxes which situate on respective sides of a boundary plane including the central light ray and perpendicular to a plane of incidence, and are reflected by the reflection surface are separately received by two light receiving regions which are divided along a boundary plane including the central light ray reflected by the reflection surface and perpendicular to the plane of incidence. The focussing error signal is derived as a difference between output signals from the two light receiving regions. A relay lens is arranged between the reflection surface of the detection prism and the light receiving regions and the relay lens forms an image of a pupil of the objective lens on the light receiving regions.

REFERENCES:
patent: 4010317 (1977-03-01), Bouwhuis
patent: 4074314 (1978-02-01), Velzel et al.
patent: 4205338 (1980-05-01), Schaefer
patent: 4296316 (1981-10-01), Tsuji et al.
patent: 4390781 (1983-06-01), Musha

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