Zoom lens system for cameras

Abstract

A zoom lens system has a zoom lens holder which varies its length as the focal length is varied. The zoom lens holder includes a fixed ring, an axially movable ring disposed within the fixed ring to which a front lens holder is screwed, and a rotatable cam ring disposed around the fixed ring. The axially movable ring is engaged with the rotatable cam ring by means of a pin fixed to the outer face of the movable ring and slidably engaged with a helical cam groove of the cam ring. The pin radially extends through an axially extending key slot provided in the fixed ring and thereby prevents the movable ring from rotating about the optical axis of the zoom lens system. As the movable ring axially moves, the cam ring is rotated. A rear lens holder is axially movable within the movable ring and is engaged with the cam ring by means of an engaging pin fixed to the rear lens holder and a helical cam groove provided in the cam ring. The engaging pin radially extends through axially extending key slots provided in the movable ring and the fixed ring respectively. An actuating ring is secured to the front lens holder to be axially moved for zooming and rotated for focusing. Hence, the front lens holder and the rear lens holder are moved in the opposite directions in a zooming operation effected by the axial movement of the actuating ring.