| 摘要 |
A front component of a varifocal camera objective, axially shiftable for focusing purposes, is provided with a lens mount held by an axially extending guide rod which is slidably received in an inner annular flange and an end wall of a lens barrel. The lens mount has a pin projecting through an axial guide slot in the lens barrel into a camming groove in a surrounding milled setting ring. A rearward extension of the guide rod, nonrotatable but axially slidable with reference thereto against the force of a tension spring, is provided with male threads engaged by a drive nut held captive in the end wall, the nut being provided with outer gear teeth meshing with a pinion which is driven by a reversible electric motor via a slipping clutch. Upon retraction of the threaded extension by the drive nut, the tension spring holds the pin of that lens mount against the rear edge of its camming groove; the width of that groove and the axial length of the guide slot are sufficient to let the motor drive the lens mount over at least part of the available focusing range in a given position of the setting ring. |
