Electronic exposure control

US4175855A · kind A · utility

Assignee

• Terminal Data Corporation · US

Inventors

• William C. Turner · Sedona, US
• William R. Limburg · Torrance, US
• John S. Burton · Los Angeles, US

Key dates

• Filing date: Jan 20, 1976
• Grant date: Nov 27, 1979
• Expiry date: Jan 20, 1996

Classification

• Technology area (CPC G): Physics
• CPC primary: G03B27/72
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

A photographic exposure control for sensing and electrically processing illumination reflected from a moving document. An opto-photoelectric pickup accepts reflected illumination having a selected spectral characteristic. Electronic analog logic; (1) samples and holds the equivalent electrical magnitude of the reflected illumination, (2) provides an electrical timing interval that is the reciprocal of the electrical magnitude, (3) arranges automatically for constant exposure of the film through an adjustable electrical ramp generator, and (4) generates an "exposure stop" signal in a comparator that receives the ramp and the reciprocal timing information. The control signal thereby formulated typically accurately actuates a translational type shutter through a stepper motor to maintain a constant density of the background of images on microfilm for successive documents regardless of the background reflectivity thereof. A "Manual" mode is alternately available for providing a fixed exposure, particularly for documents having unorthodox reflectivity formats.