Cam ring, and a zoom lens barrel with the cam ring

A zoom lens barrel comprising:

• a first movable lens frame which supports a first lens group, and includes at least one first cam follower;
• a second movable lens frame which supports a second lens group, and includes at least one second cam follower;
• a linear guide ring which is coaxially provided about an optical axis, and includes at least one linear guide slot extending parallel to said optical axis;
• and
• a cam ring which is coaxially provided around said linear guide ring, said cam ring including at least one first cam groove and at least one second cam groove;
• wherein said first cam follower and said second cam follower pass through a common said linear guide slot and engage in said first cam groove and said second cam groove, respectively, so that a rotation of one of said cam ring and said linear guide ring relative to the other causes said first movable lens frame and said second movable lens frame to move along said optical axis via engagement of said first cam follower with said linear guide slot and said first cam groove and via engagement of said second cam follower with said linear guide slot and second cam groove, respectively;
• wherein said cam ring is provided with a large ring portion, a middle ring portion having a smaller diameter than said large ring portion, a small ring portion having a smaller diameter than said middle ring portion, a first radial flange portion which is positioned between said large ring portion and said middle ring portion to connect said large ring portion with said middle ring portion, and a second radial flange portion which is positioned between said middle ring portion and said small ring portion to connect said middle ring portion with said small ring portion;
• wherein said first cam groove is formed on both said middle ring portion and said first radial flange portion so that one end of said first cam groove constitutes a first open end at said first radial flange portion, whereby said first cam follower can be inserted into said first cam groove through said first open end;
• and
• wherein said second cam groove is formed on both said small ring portion and said second radial flange portion so that one end of said second cam groove constitutes a second open end at said second radial flange portion, whereby said second cam follower can be inserted into said second cam groove through said second open end.