Patent ID: 7106527

Claim:
An image-forming optical system comprising in order from the magnifying side to the demagnifying side: a refractive optical element having a positive optical power as a whole; and a reflective optical unit comprising at least three reflective surfaces, each of the at least three reflective surfaces having a curvature; wherein the refractive optical element is separated from the reflective optical unit and is disposed further on the magnifying side than a final reflective surface of the reflective optical unit, the image-forming optical system has a pupil on the magnifying side of the reflective surface furthest on the magnifying side in the reflective optical unit, and satisfies the following conditions: T1>T2 where T 1 represents a minimum distance on a reference axis ray between the reflective surfaces in the reflective optical unit, and T 2 represents a distance on the reference axis ray from the pupil to the refractive surface furthest away from the pupil in the refractive optical element, the reference axis ray is a ray through a center of the pupil to a center of a final image-forming surface.