Patent ID: 7039308

Claim:
A cam mechanism comprising: a cam ring; and a linearly movable frame movable by the cam ring along an optical axis of an optical system without rotating, by engagement of a plurality of cam grooves located on said cam ring with a plurality of complementing cam followers located on said linearly movable frame when said cam ring is rotated, said linearly movable frame supporting at least one optical element of said optical system, wherein said plurality of cam grooves are located at different positions at least in said optical axis direction and trace substantially a same reference cam diagram; wherein all cam grooves of said plurality of cam grooves are partial cam grooves, each having at least one end opening at at least one of opposite ends of said cam ring, so as not to include an entire portion of said reference cam diagram; wherein said plurality of complementing cam followers are located at different positions at least in said optical axis direction and are respectively engageable in said plurality of cam grooves; and wherein at least one of said complementing cam followers remains engaged in a corresponding said cam groove while at least one of the other of said complementing cam followers comes out of said end opening and is disengaged therefrom, when said linearly movable frame moves to at least one of opposite limits for movement thereof in said optical axis direction.