Zoom lens device

Abstract

A movable lens barrel contains a front lens group and a rear lens group and moves along the optical axis during zooming. The front lens group moves together with the movable lens barrel during zooming, and moves relative to the movable lens barrel along the optical axis during focussing. The rear lens group moves within and relative to the movable lens barrel during zooming. A deviation of the focussing position takes place due to backlash of the drive mechanism of the movable lens barrel. This focussing position deviation is eliminated by changing the position of the front lens group as set for focussing, or by changing the position of the rear lens group as set for zooming, respectively in accordance with the zooming direction. In order to determine the set position of the front lens group, two tables are provided corresponding respectively to the zooming direction. Each table stores a plurality of lens setting positions, an optimum one of which is selected in accordance with the focal length and subject distance. In order to adjust the position of the rear lens group, two types of cam surfaces are provided which are selectively used in accordance with the zooming direction. In another embodiment, a double cam ring is provided which is rotated during zooming to determine the position of the rear lens group. Only immediately after the zooming direction changes, the double cam ring is slid along the optical axis by a predetermined amount.