Electronic system for photographic devices

Abstract

There is disclosed herein an electronic system and circuits for photographic devices for performing certain photographic calculation and control functions. In an exemplary embodiment, the system is particularly useful for performing metering, calculation and control of shutter timing and/or diaphragm aperture opening for a camera. The system includes a logarithmic converter for converting an electrical signal proportional to light intensity passing through the camera lens from a linear value to a log value, and a calculator responsive thereto and to other input parameters, such as film sensitivity, open aperture, selected aperture and selected shutter speed which, in turn, calculates an appropriate shutter speed and an appropriate aperture. The output of the calculator is connected to a circuit, which includes the log converter in a feedback loop for performing an antilog function and for controlling shutter speed and/or diaphragm aperture. The use of the same log converter for performing log and antilog operations provides compensation for errors inherent in the use of separate conversion circuits and improves accuracy and temperature stability to thereby insure accurate and stable metering. The calculator allows either or both of the shutter speed and diaphragm aperture to be calculated and controlled. In addition, a sample and hold circuit memorizes the exposure value EV to enable either shutter speed or aperture value to be changed while automatically compensating for the other.