Videodisc autofocus device

Abstract

A focusing arrangement for an optical disk system that inhibits focus servo loop operation when the optical head objective lens is outside of a focus range distance with respect to the disk. In the optical head a laser beam converged by the objective lens is projected onto the light-reflecting layer of an optical disk. The laser beam reflected from the light-reflecting layer of the disk is projected to the light-receiving surface of a photodetector through the objective lens, a light shielding plate, a projection lens and a cylindrical lens. The laser beam is then projected to the light-receiving surface of the photodetector, thus forming a pattern thereon. As the objective lens moves along its optical axis, the laser beam is deviated and the pattern moves in a specific direction. The photodetector comprises first and second photosensitive regions. When the objective lens lies at a distance shorter than a first predetermined distance from the light-reflecting layer, the pattern is formed on the first photosensitive region. When the objective lens lies at a distance longer than the second predetermined distance, the pattern is formed on the first photosensitive region. When the objective lens is located at a distance longer than the first predetermined distance and shorter than the second predetermined distance, the pattern is formed on the second photosensitive region.

Dependencies are inferred from the claim text.