Patent ID: 7549755

Claim:
A projection optical system having a magnification side and a reduction side for forming a magnified image on a magnification side image surface that is conjugate with a reduction side image surface, said projection optical system comprising, arranged in order from the reduction side: a first imaging system including a plurality of lens elements and lens components; and a second imaging system including a mirror having a concave, aspheric reflecting surface; wherein an intermediate image is formed between said first imaging system and said second imaging system; said first optical system includes an optical axis; all the optical elements of said first imaging system are rotationally symmetric about said optical axis; and the following condition is satisfied: 1.7<|( L ·tan θ1)/ Y|< 2.8 where θ 1 is the maximum angle among all the angles that principal rays from said first imaging system to said second imaging system make with the normal to said reduction side conjugate image surface; L is the distance along said optical axis from said reduction side conjugate image surface to the closest lens element of said first imaging system; and Y is the distance from the intersection of said optical axis and said reduction side conjugate image surface to the image point of said reduction side conjugate image surface that is farthest from said intersection.