Patent ID: 7164854

Claim:
A cam mechanism comprising: a cam ring; and a linearly movable frame movable by said cam ring along an optical axis of an optical system, by engagement of a plurality of cam groove groups located on said cam ring with a plurality of cam follower groups 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 groove groups are located at different positions in a circumferential direction of said cam ring, and wherein each said cam groove group comprises at least two cam grooves located at different positions in at least said optical axis direction and respectively trace substantially a same reference cam diagram; wherein at least one of said two cam grooves of one said cam groove group intersects with another of said two cam grooves of another said cam groove group, said another said cam groove adjacent to said at least one said cam groove in said circumferential direction; wherein said plurality of cam follower groups are located at different positions in a circumferential direction of said linearly movable frame, and wherein each cam follower group comprises at least two complementing cam followers located at different positions in said optical axis direction and are engageable with said at least two cam grooves of each said cam groove group, respectively; and wherein in each said cam groove group, at least one of said at least two complementing cam followers of each said cam follower group remains engaged in a corresponding one of said at least two cam grooves when another cam follower of said at least two complementing cam followers passes through an intersection area of said intersecting cam grooves during a rotation of said cam ring.