The optical system is characterized by a rotationally symmetric front group that is located on a single axis of rotational symmetry passing through the center of an image plane, a rotationally symmetric back group, and an aperture, wherein the front group includes two internal reflecting surfaces and two transmitting surfaces, a light beam incident from at least one object plane on the front group forms an optical path along which the light beam enters a first transmitting surface, is reflected off a first reflecting surface and then off a second reflecting surface, and exits out of a second transmitting surface, and the light beam passes through the back group and aperture and is imaged in a position of the image plane away from the axis of rotational symmetry without being intermediately imaged within a section including the axis of rotational symmetry.
