Patent ID: 7693417

Claim:
An optical option attachment ring comprising: a ring body that connects one end to the other end, receives a lens barrel, and has a predetermined gap between the one end and the other end; a fastening screw that is inserted into screw holes that pass through the one end and the other end; a rotator having an abutting surface that projects inward from the inner circumferential surface of the ring body and abuts the front end of the lens barrel as well as an arcuate portion that follows the upper end of the abutting surface; a resilient member that applies an urging force to the rotator such that the rotator rotates in the direction opposite to an insertion direction of the lens barrel; and a stopper that abuts at least one of the one end and the other end so as to restrict the rotation caused by urging force of the resilient member, wherein the one end and the other end, the ring body and the fastening screw are configured such that tightening the fastening screw brings the one end and the other end closer to each other and hence the diameter of the ring body decreases so that the optical option attachment ring is fastened to the lens barrel, while loosening the fastening screw separates the one end and the other end from each other and hence the diameter of the ring body increases so that the optical option attachment ring disengages from the lens barrel, the rotator is configured such that when the lens barrel is inserted into the ring body and moved to a predetermined position, the front end of the lens barrel abuts the abutting surface and the front end of the lens barrel moves relative to the abutting surface so as to rotate the rotator, so that the abutting surface and the arcuate portion are situated outside the inner circumferential surface of the ring body, and when the lens barrel is inserted into the ring body and moved to the predetermined position, the urging force of the resilient member rotates the rotator so that the abutting surface and the arcuate portion are situated in a groove formed in the lens barrel.