Patent ID: 7880972

Claim:
A projection optical system for projecting, while enlarging, an image formed on an image formation surface onto an image projection surface obliquely relative to the image projection surface, the projection optical system comprising: a plurality of curved reflective surfaces including at least a first convex reflective surface; and at least one aberration correcting refractive surface, wherein at least one of the aberration correcting refractive surface fulfills conditional formula (4b) below, and is located in an optical path on an enlargement side of the first convex reflective surface as counted from a reduction side, and a most enlargement-side curved optical surface is a reflective surface: 1.1 <Lr/La <2 (4b) where, let a ray traveling from an image center on the image formation surface through a center of a pupil to an image center on the image projection surface be called a “reference ray”, La represents a distance from the image formation surface to the pupil along the reference ray; and Lr represents a distance from the image formation surface to the aberration correction refractive surface along the reference ray.