Patent ID: 8025415

Claim:
A projection optical system in which plural light beams emitted from an image forming element displaying image information on a conjugate plane A are allowed to be obliquely incident on a conjugate plane B so as to form an enlarged image of an image formed by the image forming element on the conjugate plane B, wherein the projection optical system comprises, at least, a first optical system, a second optical system, an intermediate image of the image forming element between the first optical system and the second optical system on which the plural light beams are generally converged, an optical system having a refractive power in the first optical system being composed of only a lens system transmitting the light beams, the intermediate image being formed by only a refractive power of the first optical system, the second optical system being a reflective optical system comprising a reflection mirror having a positive refractive power which reflects the light beams and is directly behind the intermediate image, the first optical system is divided into a first lens group, a second lens group, and a third lens group by a stop and the third lens group includes a maximum lens distance space at the side of the conjugate plane B from the stop, and the first lens group, the second lens group, and the third lens group have respective positive, positive, and negative refractive powers in sequence from the side of conjugate plane A.