Adjusting mechanism for optical objective with lost-motion zone

摘要

In order to establish a predetermined position of focusing or focal-length adjustment for an optical objective, a mechanism for the axial shifting of one or more lens members has a lost-motion zone in its operating range in which a continuing displacement of a control element does not change the focal length and/or distance of the objective. The halting of the lens shift (or, possibly, a compensatory displacement of an otherwise stationary lens member) can be brought about mechanically, with the aid of suitably shaped cam tracks, or electromechanically, via analog or binary position sensors. Arrival of the adjusting mechanism in the lost-motion zone may be signaled to the user by a detent, by a change in frictional resistance, or by a visual or acoustical indicator.