Exposure control circuit

Abstract

This invention relates to photographic cameras, and more particularly to an exposure control circuit of the type in which an analog output representative of the object brightness level is converted to a digital signal which is factored into an exposure value, and the period of actuation of the camera shutter is controlled in accordance with this exposure value. Still more particularly, it relates to an improvement over this conventional type exposure control with respect to the A-D conversion. The prior art converts a voltage representative of the object brightness to a digital form by the use of an A-D converter such as of the follow comparison type which is characterized by the lack of integrating aspect in converting the input voltage to the corresponding digital signal. Therefore, when the illumination for the object being photographed is caused to flicker in a period of time shorter than the effective exposure time interval, an alternating current component is introduced into the input voltage of the converter. Accordingly, it is made impossible to effect accurate exposure control based on the digital signal representing the only object brightness level. The invention provides an exposure control circuit which is not susceptible of this alternate current component as it is removed in the course of the A-D conversion.