Unidirectional focussing system

US4303319A · kind A · utility

Assignee

• Agfa-Gevaert NV · BE

Inventors

• August Hell · Straubing, DE
• Istvan Cocron · Munich, DE

Key dates

• Filing date: Jun 26, 1979
• Grant date: Dec 1, 1981
• Expiry date: Jun 26, 1999

Classification

• Technology area (CPC G): Physics
• CPC primary: G02B7/34
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

At the start of each focussing operation, the camera objective is at a first extreme subject-distance setting and is moved in a first direction therefrom towards the second extreme subject-distance setting. A focus-evaluating circuit comprises first and second photodetectors located to receive light from the subject and a comparing circuit which compares the light incident on the photodetectors and in dependence upon the present subject-distance setting generates first and second signals respectively indicating that the subject-distance setting should be changed in the first direction or in the opposite second direction, such circuit having bidirectional character and furthermore establishing a tolerance range of acceptable distance-setting error within which both the first and second signals are generated. During the unidirectional change of subject-distance setting, the appearance of the first signal leads to generation of a stop signal commanding that the progressive change of distance setting be stopped. Accordingly, the unidirectional change of setting is commanded to stop at the point where the changing distance setting just enters into the tolerance range of the bidirectiona…