Zoom lens focusing apparatus

摘要

A zoom lens focusing apparatus for a camera includes a zoom ring for adjusting a zoom lens section of the camera to different magnifications by moving a movable lens assembly therein forward and backward. A cam mechanism couples the zoom ring to the movable lens assembly, so that a change in the focal length of the zoom lens section caused by rotation of the zoom ring, is a logarithmic function of the angle of rotation of the zoom ring. A master lens section of the camera also has a movable lens assembly therein which is movable forward and backward by a driving device. The position of the zoom ring is detected while the movable lens of the zoom lens section moves backward or forward, and a sampling pulse generating circuit produces a pulse corresponding to the position of the zoom ring. A voltage which changes corresponding to the distance of the subject from the camera is applied to a charge-and-discharge circuit and the output thereof is held in a sample and hold circuit. The driving device is driven by the output held to drive the movable lens assembly of the master lens section to thereby attain focusing.