The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 19, 1984
Filed:
Aug. 14, 1981
Olympus Optical Co. Ltd., , JP;
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.