Focus detecting device switching between passive and active detection

摘要

A focus detecting device switchable between an active and a passive mode has a passive mode in which light from an object is accumulated in a light accumulation type receiving portion without light from a light source being projected onto the object, and an active mode in which light from a light source is projected onto the object. The light accumulated in the accumulation type receiving portion is used to effect focus detection. An accumulating control circuit is provided for controlling the accumulation operation performed by the light receiving portion. A processing circuit is provided for performing the focus detection calculations on the basis of the accumulated output of the light receiving portion as controlled by the control circuit. A change-over circuit is provided for automatically changing between the passive and active modes on the basis of the accumulation state during the accumulating operation before the control of the accumulation operation by the control circuit is terminated.