Patent ID: 6951395

Claim:
A projection optical system which provides a final image of an original image formed by an image forming element on a final image plane, the projection optical system comprising: a plurality of reflecting surfaces, each of the surfaces having a curvature, wherein a central principal ray, which is a principal ray of luminous flux traveling from a center of the original image to a center of the final image, enters obliquely on the final image plane, and the projection optical system forms an intermediate image of the original image between the original image and the final image in a path of the central principal ray, and a final pupil plane, which is closest to the final image plane of a plurality of pupil planes being between the original image and the final image, is arranged on the original image side with respect to a final reflecting surface, which is closest to the final image plane of the plurality of reflecting surfaces, and the following expression is satisfied: 0<( S 0 ×|β|)/ S 1 <8 where S 0 represents a length of a path of the central principal ray from the final pupil plane to the final reflecting surface, S 1 represents a length of a path of the central principal ray from the final image plane to the final image plane, and β represents a magnification of the final image with respect to the original image in a plane including a normal to the final image plane and the central principal ray entering on the final image plane.