Automatic focussing system for photographic cameras

US3988747A · kind A · utility

Assignee

• AGFA-Gervaert AG · DE

Inventors

• Peter Lermann · Feldkirchen-Westerham, DE
• Stefan Vogt · Jena, DE
• Alois Rieder · Munich, DE

Key dates

• Filing date: Feb 28, 1975
• Grant date: Oct 26, 1976
• Expiry date: Feb 28, 1995

Classification

• Technology area (CPC G): Physics
• CPC primary: G02B7/36
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

A prism positioned behind the objective rotates at a predetermined frequency. The pulsed light beam produced thereby is split into a first and second pulsed beam, each falling on a photoelectric transducer element. The first photoelectric transducer element is positioned at a distance from the objective which is less than the distance between the film plane and the objective plane by a predetermined distance. The second photoelectric transducer is positioned away from the objective by a distance exceeding the distance between the film plane and the objective plane by the same predetermined distance. The first and second electrical signals produced by the first and second photoelectric transducer are differentiated and stored. The so-stored signals are compared and a control signal for driving a motor in a first or second direction is furnished corresponding to the difference therebetween. The motor drives the objective either closer to or away from the film plane in response to the control signal.