1. Field of the Invention
This invention relates to a zoom lens barrel, and more particularly to a zoom lens barrel in which flange back adjustment can be easily carried out by use of a simple mechanism.
2. Description of the Related Art
When manufacturing a photographic camera with a zoom lens, flange back adjustment is carried out for correcting deviation of a focal point due to fluctuation in lens properties, precision in a lens drive cam and the like, thereby positioning the focal point of the zoom lens on the film surface.
As a method of carrying out the flange back adjustment, there has been proposed a method in which a fixed barrel is linearly moved back and forth by rotating a rotary barrel to move the overall lens groups in the direction of optical axis, as disclosed for instance in Japanese Unexamined Patent Publication No. 7(1995)-134235.
However this approach is disadvantageous in that a rotary barrel which is used only for the flange back adjustment is provided and adds to the overall size of the barrel.
In the case of a camera with a zoom lens which comprises a front lens group and a rear lens group disposed along the optical axis and in which both the front and rear lens groups are moved in the direction of the optical axis for zooming and only the front lens group is moved in the direction of the optical axis by an actuator provided in a shutter block for focusing, it is conceivable that the front lens group is moved in the direction of the optical axis by the actuator during each focusing by a distance which can compensate for deviation of the focal point. However this approach is disadvantageous in that the movement of the actuator must be enlarged, which adds to the cost of the shutter block.