Abstract: An optical system includes an aperture stop and binary optics having a plurality of rings disposed adjacent to the aperture stop. The rings of the binary optics have different mutual intervals and have a step-like structure formed at each interval. When the interval of arbitrary rings of the rings, which are juxtaposed with each other, is T and the number of steps defined in that interval is N, the following relation is satisfied in all the rings included in the binary optics 16≧N≧T·sin &thgr;h/&lgr;, where &lgr; is a representative value for a wavelength of light used in the optical system, and &thgr;h is an angle defined, with respect to an optical axis of the optical system, by a light ray emitted from an object point at a largest object height and passing a center of the aperture stop.