One-hand zoom lens barrel

Claim 1

A lens barrel adapted to be used in a zoom lens system of the two-group type which achieves zooming by moving front and rear lens units in the direction of an optical axis of said lens units and which achieves focusing by displacing the front lens unit in the direction of the optical axis, said barrel comprising: (a) a front lens unit frame (1) for holding a front lens unit; (b) a front lens unit moving frame (4) onto which said front lens unit frame is threaded; (c) a rear lens unit frame (2) for holding a rear lens unit; (d) a single operating sleeve (6) that can be rotated or displaced in the direction of the optical axis and which is coupled to said front lens unit frame, whereby turning said operating sleeve causes said front lens unit frame to rotate; (e) a sliding ring (5) that is movable en masse with said single operating sleeve in the direction of the optical axis; (f) a cam sleeve (3) that has a first cam groove (3a) to permit said sleeve to rotate in operative association with the linear movement of said sliding ring; (g) a second cam groove (4a) for said front lens unit that allows said front lens unit moving frame to be displaced in the direction of the optical axis as a result of the rotation of said cam sleeve; and (h) a third cam groove (3b) for said rear lens unit that allows said rear lens frame to be displaced in the direction of the optical axis as a result of the rotation of said cam sleeve, wherein said first, second and third cam grooves are shaped to satisfy the following relation over an entire zoom range of the lens system: tan θ.sub.F +tan θ.sub.R +tan θ.sub.Z =K, where θ Z is the angle, with respect to the optical axis, of the first cam groove for a small change in focal length of the lens system; θ F is the angle, with respect to the optical axis, of the second cam groove for a small change in the focal length; θ R is the angle, with respect to the optical axis, of the third cam groove for a small change in the focal length; K is a constant.