Automatic focusing apparatus

Abstract

Disclosed is an automatic focusing system for optical imaging equipment, such as a camera, which includes a relative image displacement detection system providing first and second digital quantities indicative of the direction in which the focus of the imaging system is to be altered to achieve focus and the magnitude of such alterations, respectively, and an image contrast detection system providing a third digital quantity indicative of the change in the contrast of an image formed by the imaging system as the focus thereof is altered. In addition, the apparatus includes a servomotor for altering the focus of the imaging system and a motor control circuit which receives the first, second and third digital quantities and provides motor control signals to the servomotor. The motor control circuit initially responds to the first and second digital quantities from the relative image displacement detector and provides appropriate motor control signals for altering the focus of the imaging system under the control of the relative image displacement detection system until the change in image contrast as indicated by the third digital quantity becomes negative. Thereafter, the motor control circuit responds to the third digital quantity and provides appropriate motor control signals to alter the focus of the imaging system under the control of the image contrast detection system until the magnitude of the third digital quantity becomes less than a predetermined value.