Servo focus drive for lens - has spring return and solenoid hold on ratchet

摘要

The servo focus drive for a lens has the lens mounted in a ring (12) sliding inside the focus tube (14). A spring (16) presses the mounting ring against a stop (13) at one end of the focal range while a linear drive motor (50) pushes the ring against the spring pressure. The wall of the focus tube has a ratchet (40) in an axial slot with a solenoid operated catch (42,28) on the mounting ring to hold the set position. The release of the ratchet solenoid allows rapid return action of the mounting ring to the preset position on the stop. The return action, and the linear drive action, provide a rapid focus setting without hunting and with a simple layout. The set position is held without any power and the whole drive operates with a minimum of power drain.