Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1977-05-19
1978-10-31
Dahl, Lawrence J.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
1791003V, 358128, G01J 136
Patent
active
041236521
ABSTRACT:
An apparatus is described for reading a record carrier with an optical information structure, in which apparatus errors in the focussing of a read beam on the information plane are detected with an astigmatic focussing-error detection system.
By including a beam splitter in the path of a beam which has been reflected by the record carrier and by including an astigmatic focussing-error detection system in each of the paths of the two sub-beams thus obtained, the astigmatism of the one detection system being opposed to that of the other detection system, a focussing-error signal can be derived which is independent of optical faults in the read apparatus.
REFERENCES:
patent: 3719421 (1973-03-01), Poilleux et al.
patent: 4023033 (1977-05-01), Bricot et al.
patent: 4025949 (1977-05-01), Whitman
patent: 4059841 (1977-11-01), Bricot et al.
Cohen Simon L.
Dahl Lawrence J.
Trifari Frank R.
U.S. Philips Corporation
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