Control mechanism for varifocal objective and the like

Claim 1

A CONTROL MECHANISM FOR THE DIFFERENTIAL DISPLACEMENT OF A PAIR OF OPTICAL ELEMENTS ALONG A COMMON AXIS, COMPRISING GUIDE MEANS FOR SAID ELMENTS ENABLING MOVEMENT THEREOF ALONG SAID AXIS, A GENERALLY CYLINDRICAL CONTROL MEMBER ROTATABLE ABOUT ITS AXIS, SAID MEMBER HAVING GENERATRICES PARALLEL TO SAID COMMON AXIS AND BEING PROVIDED ON A PERIPHERAL SURFACE WITH AT LEAST ONE RELATIVELY NARROW GROOVE FORMING A LEADSCREW TRACK OF CONSTANT PITCH AND A RELATIVELY WIDE GROOVE FORMING A LEADSCREW TRACK OF VARYING PITCH OVERLAPPING EACH OTHER ON A PART OF SAID SURFACE, FIRST FOLLOWER MEANS ON ONE OF SAID ELEMENTS MATINGLY ENGAGING IN A PLURALITY OF TURNS OF SAID TRACK OF CONSTANT PITCH, SECOND FOLLOWER MEANS ON THE OTHER OF SAID ELEMENTS MATINGLY ENGAGING IN SAID RELATIVELY WIDE GROOVE, THE WIDTH OF SAID FIRST FOLLOWER MEANS EXCEEDING THAT OF SAID RELATIVELY WIDE GROOVE, AND MEANS FOR ROTATING SAID CONTROL MEMBER ABOUT ITS AXIS.