Abstract: Optical apparatus comprises an optical element and a moving mechanism having two members arranged to move the optical element in the direction of an optical axis thereof by moving one of the two members in the direction of the optical axis relative to the other while rotating said two members relative to each other. The two members include a male helicoid member having a male helicoid screw and a female helicoid member having a female helicoid screw arrangement in screw engagement with the male helicoid screw, the female helicoid screw arrangement providing only a single screw thread peripherally interiorly of the female helicoid member along an axis parallel to the optical axis.