For a variable focus objective is to develop very rapprochee

摘要

This method and this device relate to variable-focus objectives comprising a category of two sets II and III of lenses providing the variation in the focal length as they are moved axially, and another category of at least one set I or V of lenses whose movement along the axis causes a variation in the object focusing distance. In order to focus on an object very close to the objective, not only is the group or groups I, V of lenses of the category providing the focusing moved, but the groups II and III of lenses of the category normally providing the sole variation in the focal length are simultaneously moved, so as to compensate for a parasitic variation in the apparent field which, without it, would occur in such a case. For this purpose, the two systems for controlling the device are slaved to each other, so that, for focusing on an object very close to the objective, the focusing-control system acts on the system for controlling the sets II and III of lenses of the first category so as to move them simultaneously. IMAGE