APPARATUS FOR READING A FLAT RECORD CARRIER WITH AN OPTICALLYREADABLE INFORMATION STRUCTURE

摘要

An apparatus is described for reading a flat record carrier on which information is stored in an optically readable track-shaped information structure. By the arrangement in the far field of the information structure and at one side of a plane which is formed by the optical axis of an objective system which is used for reading and a line parallel to the center line of the track portion to be read, of a radiation-sensitive detection system which consists of at least two detectors in approximately the position beta /2, beta being the angle at which a first-order beam is diffracted in the lateral direction of the tracks, centering and focussing errors can be detected without the use of auxiliary beams and additional optical elements.