Automatic exposure time control circuitry for a camera using a photodiode as a light measuring element
US3936842A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 21, 1974 |
| Grant date | Feb 3, 1976 |
| Priority date | — |
| Expiry date | Jun 21, 1994 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03B7/083
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
A light measuring circuit for an exposure time control device uses a photodiode to measure the object brightness and a logarithmic compressing diode to provide negative feedback between the output terminal and one input terminal of a differential amplifying circuit. The output of the light measuring circuit is summed with signals representing film sensitivity and diaphragm aperture setting and the resulting exposure time control signal is compensated for changes in temperature. An antilogarithmic converting circuit generates a signal proportional to the logarithmic value of the compensated exposure time control signal. The antilogarithmic converting circuit operates at the same reference potential as the differential amplifying circuit and its output is integrated and then used to terminate exposure.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.