Zoom lens device

摘要

A zoom lens device has a helical movement barrel and a drive ring mounted in a fixed barrel to be rotatable about an optical axis. The helical movement barrel holds front and rear lens groups therein. The drive ring is rotated by a motor through gears. The drive ring is coupled to a helical movement barrel with a clearance in the circumferential direction, so the drive ring can rotate relative to the helical movement barrel within an angle defined by the clearance. While the drive ring rotates relative to the helical movement barrel, the rotational movement of the drive ring causes a cam barrel to move along the optical axis relative to the helical movement barrel. The axial movement of the cam barrel causes the rear lens group to move along the optical axis. When the drive ring is rotated beyond the angle defined by the clearance, the rotational movement of the drive ring causes the helical movement barrel to rotate together with the cam barrel. As the helical movement barrel moves along the optical axis while rotating, the front and rear lens groups moves along the optical axis. The rear lens group moves relative to the front lens group with the rotation of the cam barrel.