Patent ID: 6867922

Claim:
A projection optical system for projecting an image of an object onto an image plane, said projection optical system including, in order from an object side, a first lens group having a positive refractive power and a second lens group having a negative refractive power, said projection optical system comprising: two aspherical surfaces being disposed at positions satisfying a relation 15>|h b /h|>0.35 where h is a height of an axial marginal light ray and h b is a height of a most abaxial chief ray, wherein a relation 0.02>|ΔASPH/L|>1.0×10 −6 is satisfied where ΔASPH is an aspherical amount of each aspherical surface and L is a conjugate distance of said projection optical system, wherein said two aspherical surfaces include regions in which, from a central portion to a peripheral portion of the surface, their local curvature powers change with mutually opposite signs, wherein a relation 70>|L×φ 0 |>17 is satisfied where, in the case that said projection optical system has only one negative lens group, φ 0 is the power of the negative lens group of said projection optical system, and in the case that said projection optical system has more than one negative lens group, φ 0 is the total power of the negative lens group of said projection optical system, and wherein one of said two aspherical surfaces is provided in said first lens group and the other aspherical surface is provided in said second lens group, or both of said two aspherical surfaces are provided in said second lens group.