Method and apparatus for detecting focussing error signal of obj

Details Method and apparatus for detecting focussing error signal of obj Method and apparatus for detecting focussing error signal of obj

1980-10-08

1983-06-28

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 45, G01J 136

Patent

active

043907814

ABSTRACT:
In a method 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.

REFERENCES:
patent: 4357533 (1982-11-01), Winslow

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