JPS5773707A - Focusing device - Google Patents

Abstract

PURPOSE:To achieve easy, secure focusing with simple constitution by determining an in-focus position by an out-of-focus signal obtained from two image pickup outputs when an optical system lens is moved with an optical path length difference held constant. CONSTITUTION:Object light passed through a convex lens 11 is incident to image sensors 161 and 162 at positions conjugate with corresponding image position before and behind a film surface 13 by way of optical paths having a constant optical path length difference between half-mirror 141 and a total-reflection mirror 142, thereby forming picture elements 161a and 162a. Then, a signal processor 15 calculates the square sum of a difference between outputs of those sensors 161 and 162 to determine an out-of-forcus signal, and the movement of the lens 11 is controlled to minimize the out-of-focus signal, thus performing focusing. Therefore, it is unnecessary to store the out-of-focus signal at each lens position, and the magnitude of the out-of-focus signal does not depend upon a space frequency on sensor surfaces; and the dynamic range is decreased by minimizing processing, and easy, secure focusing is achieved with simple constitution.