Claims
- 1. An apparatus for reading a record carrier on which information is stored in an optically readable structure, which apparatus includes a radiation source, an objective system for imaging the radiation source on the information structure of the record carrier, a radiation-sensitive detection sstem for converting the radiation which is supplied by the radiation source and modulated by the information structure into an electrical signal, said apparatus being provided with a focus error detection system, wherein the radiation source comprises at least two radiation sub-sources, which are offset relative to each other both in the direction of the optical axis of the objective system and in a direction transverse thereto, a separate detector in the detection system for each of the radiation sub-sources, a first element means for dividing a radiation beam supplied by the radiation source into two separate sub-beams, a second element means for focussing the sub-beams in different planes, an optical assembly comprising an optical wedge and a field lens disposed in the path of the radiation passing said separate detectors, and at least three additional radiation-sensitive detectors disposed in the plane in which images of the exit pupil of the objective system are formed by the optical assembly, wherein the radiation - sensitive detection system detects small errors in focusing and the additional radiation - sensitive detectors derive correction signals for large focusing errors.
Priority Claims (1)
Number |
Date |
Country |
Kind |
7402504 |
Feb 1974 |
NL |
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Parent Case Info
This application is a continuation-in-part of U.S. Pat. Application Ser. No. 527,244, filed Nov. 26, 1974, now U.S. Pat. No. 3,992,575 issued Nov. 16, 1976.
US Referenced Citations (7)
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
527244 |
Nov 1974 |
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