| 摘要 |
PHN 829 1 3.3.76 An apparatus is described for reading a record carrier, on which information, for example video and/or audio information, is stored in an optically readable track-shaped information structure. Errors in the focussing of a read beam relative to the plane of the information structure can be detected with the aid of two detectors which are disposed in the far field of the information structure, which detectors are arranged at one side of a plane defined by the optical axis of an objective system and a line which effectively extends transversely to the track direction and which longitudinal direction are effectively transverse to the track direction. With the aid of the same detectors a reference signal is obtained, which is employed for deriving a control signal for focussing correction of the read beam. |
