Patent ID: 8228625

Claim:
An optical apparatus comprising: a lens barrel inside which a lens is provided, the lens barrel including a lens-side mounting unit; an optical apparatus body to which the lens barrel is attached, the optical apparatus body having an optical axis that coincides with an optical axis of the lens; a body-side mounting unit that is provided on the optical apparatus body, the body-side mounting unit having a cylindrical part and a flange part, the flange part being formed adjacent to or at one end of the cylindrical part; said lens-side mounting unit that has a cylindrical shape, the lens-side mounting unit being mounted on the outside of the cylindrical part of the body-side mounting unit, the lens-side mounting unit being turned thereon so as to be attached to the body-side mounting unit; and a position determination mechanism that determines a position of the lens-side mounting unit around the optical axis of the optical apparatus body, wherein a plurality of projection pins that protrudes from an outer circumferential surface of the cylindrical part is provided on the outer circumferential surface in a circumferential direction, a groove is formed in an inner circumferential surface of the lens-side mounting unit in the circumferential direction, and cutout regions that are in communication with the groove are formed in a surface of the lens-side mounting unit that faces toward the flange part of the body-side mounting unit at positions that respectively correspond to positions of the projection pins.