Method of controlling the zoom lens assembly

Abstract

A method of controlling the focusing of a zoom lens which has a plurality of lens groups including at least one focusing lens group, wherein an amount of deviation from focus caused by a zoom operation is corrected by movement of the focusing lens group. The method includes setting a reference object distance, at which no deviation from focus occurs during zooming of the zoom lens, at a finite object distance, such that the amount of movement of the focusing lens group necessary to effect focusing is determined based upon a reference position corresponding to a position of the focusing lens group at the reference object distance, in accordance with focal length data and object distance data. The zoom lens assembly includes a stationary lens barrel and a rotatable cam ring which is supported on the stationary lens barrel for movement in the direction of the optical axis while being rotated, and which includes at least two cam grooves. The zoom lens includes first and third lens groups which are both movable by one of the two cam groups in a direction of an optical axis. A second lens group movable by a second of the two cam grooves in a direction of the optical axis is also provided, as well as a focusing mechanism for moving the second lens group to a position which is determined by focal length data derived from actual positions of the first, second, and third lens groups and object distance data detected by the object distance measuring device.