Drive apparatus for zoom lens barrel

Abstract

A drive apparatus for a zoom lens barrel having at least two movable lens groups, one of which is used also as a focusing lens group, comprising a pair of lens frames which respectively hold the two movable lens groups, a pair of driven pins which are integrally provided on the lens frames, a drive cam plate which is provided with a pair of cam surfaces which engage with the corresponding driven pins and which is rotatable about an axis, a drive mechanism which includes a motor for driving the drive cam plate, and a detection mechanism which detects the angular position of the drive cam plate. One of the cam surfaces that corresponds to the movable lens group, other than the focusing lens group, is defined by a stepped cam surface having discrete sections which are adapted to set the focal length discretely, so that no movement of the movable lens group takes place in the range of the angular position of the drive cam plate corresponding to the discrete sections. The other cam surface that corresponds to the movable lens group that functions not only as the zooming lens group but also as the focusing lens group is defined by a continuous cam surface which is adapted to move the movable lens group continuously when the drive cam plate is rotated in accordance with the object distance. The stop position of the drive cam plate during the zooming operation and the angular position of the drive cam plate during the focusing operation is controlled by the detection mechanism of the angular position of the drive cam plate.