Patent ID: 6717744
Filing Date: 2004-04-06
Classification: G02B

Abstract:
A lens barrel comprising:an optical system including a front lens group and a rear lens group; a front lens frame which supports said front lens group, said front lens frame including a first cam follower and being guided linearly in an optical axis direction without rotating about said optical axis; a rear lens frame which supports said rear lens group and includes a second cam follower; and a cam ring which is driven to rotate about said optical axis and includes a cam groove in which said first cam follower and said second cam follower are engaged; wherein said cam groove of said cam ring includes a front-lens-group accommodation portion which accommodates said first cam follower, and a rear-lens-group-accommodation portion which accommodates said second cam follower and is positioned closer to the front side of said cam ring than said front-lens-group accommodation portion, said front lens group and said rear lens group being positioned in respective accommodation positions thereof when said first cam follower and said second cam follower are engaged in said front-lens-group accommodation portion and said rear-lens-group-accommodation portion, respectively; wherein one of said front lens frame and said rear lens frame includes a linear guide groove which extends parallel to said optical axis and a wide-width engaging portion which communicatively connects to a front end of said linear guide groove, said wide-width engaging portion having a greater width than said linear guide groove in a circumferential direction of said one of said front lens frame and said rear lens frame; wherein the other of said front lens frame and said rear lens frame includes a linear guide projection which is selectively engaged in one of said linear guide groove and said wide-width engaging portion; wherein said cam groove of said cam ring further includes a straight connecting portion formed so as to extend between said front-lens-group accommodation portion and said rear-lens-group-accommodation portion to extend linearly in a direction inclined with respect to both said optical axis and a circumferential direction of said cam ring, a width of said straight connecting portion being substantially the same as a diameter of said second cam follower; wherein said rear-lens-group-accommodation portion is formed as a dead end of said cam groove which only allows said second cam follower to move toward said straight connecting portion therefrom; wherein said linear guide projection is engaged in said wide-width engaging portion to thereby allow said rear lens frame to rotate with respect to said front lens frame when said front lens group and said rear lens group are positioned in said respective accommodation positions; wherein in the case where said cam ring rotates when said front lens group and said rear lens group are positioned in said respective accommodation positions, said second cam follower is rotated together with said cam ring, said second cam follower being positioned in one of said rear-lens-group-accommodation portion and said straight connecting portion in the vicinity of said rear-lens-group-accommodation portion when said linear guide projection reaches said front end of said linear guide groove from said wide-width engaging portion to be thereby prevented from rotating with respect to said front lens frame; and wherein said second cam follower is moved on a side edge of said straight connecting portion toward said front-lens-group accommodation portion so that said linear guide projection enters said linear guide groove to be properly engaged therein after said linear guide projection reaches said front end of said linear guide groove from said wide-width engaging portion.