Patent ID: 7778538

Claim:
A lens barrel having an optical system capable of change of a focal length, comprising: a diaphragm device which controls a light amount of light incident to the optical system and passing to an image forming surface; and an open F value varying device which is provided separately from the diaphragm device, controls a light amount of the light incident to the optical system and passing to the image forming surface and varies an open F value by limiting the light amount so that the open F value becomes a value according to a focal length of the optical system when the light amount which is controllable by the diaphragm device is at the maximum, the open F value varying device including a base plate substantially perpendicular to and centered about an optical axis of the optical system, the base plate including a plurality of base pins, a cam plate substantially perpendicular to and centered about the optical axis, the cam plate including a plurality of cam grooves disposed around the optical axis, the plurality of cam grooves being divided into two groups, one group having a position spaced a first radial distance away from a center of the cam plate, and a second group having a position spaced a second radial distance, greater than the first radial distance, away from the center, and a plurality of blades, each blade of the plurality of blades attached to one base pin of the plurality of base pins and including a cam pin projected from a face of the blade and engaged in one of the plurality of cam grooves, the plurality of blades rotating about the base pins according to rotation of the cam plate and a shape of the cam grooves.