Programmed automatic exposure control circuitry

Abstract

In a photographic camera capable of programmed automatic exposure control, circuitry is provided for also enabling exposure time-preferred automatic diaphragm control and diaphragm-preferred automatic exposure time control. The diaphragm is settable to an initial aperture size, which may be the fully opened aperture, and is capable of being changed to different aperture sizes. A first signal is generated in accordance with the logarithm of the light intensity measured through the diaphragm. A second signal is generated in accordance with a manual exposure time setting circuit. A third signal intermediate the first and second signals is generated with a predetermined ratio between the difference of the first and third signals with respect to the difference between the third and second signals. The diaphragm is set by determining the difference from the initial aperture size to the aperture size to be set in accordance with either the difference between the first and third signals or the difference between the third and second signals with the diaphragm at its initial aperture size. The exposure time is controlled commensurate with the diaphragm aperture set by the diaphragm aperture setting mechanism. An indicator indicates the F-number or exposure time, respectively, in accordance with the mode of operation.