Opto-electronic focus detection system
AssigneeU.S. Philips Corporation
InventorsGerrit Berend Gerritsen, Gerard Eduard VAN Rosmalen
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Abstract
In an opto-electronic focus detection system for determining a deviation between the plane of focussing of an objective and a radiation-reflecting surface the path of a focussing beam which is reflected by said surface includes an assembly of two radiation-sensitive detection elements. The difference in the output signals of said elements is proportional to said deviation. By disposing a lenslike element of which only the outer zone has a lens action before the detection elements, the measuring range can be extended while maintaining the sensitivity for small deviations.
Claims6
An opto-electronic focus-detection system for use in an apparatus for writing information in an information surface of a record carrier body as an optically readable radiation-reflecting structure with a writing beam, comprising an objective system for focussing said writing beam on said carrier body, a radiation source which emits a narrow focus detecting beam passing eccentrically through said objective of the write apparatus, two radiation-sensitive detection elements for intercepting the focus detecting beam which is reflected by the record carrier body and which passes the objective for a second time after said reflection, and a lens like element in the path of the reflected focus detecting beam to the radiation-sensitive detection elements, only the outer zone of said lens like element having a lens action, and the central part of said lens like element passing said focus detecting beam without affecting the direction of the focus detecting beam.
An opto-electronic focus-detection system for use in an apparatus for reading information contained in an information surface of a record carrier as an optically readable radiation-reflecting structure with a reading beam, comprising an objective system for focussing said reading beam on said record carrier, a radiation source which emits a narrow focus detecting beam passing eccentrically through said objective of said record carrier reading apparatus, two radiation-sensitive detection elements for intercepting the focus detecting beam which is reflected by the record carrier and which passes the objective for a second time after said reflection, and a lens like element in the path of the reflected focussing beam to the radiation-sensitive detection elements, only the outer zone of said lens like element having a lens action, and the central part of said lens like element passing the focus detecting beam without affecting the direction of the focus detection beam.
Dependencies are inferred from the claim text.