Patent ID: 7561787

Claim:
A reduction optical system for forming, without re-imaging, a reduced image of a subject image formed by a main lens system, wherein a meniscus single-lens element convex to an object side is provided on a most object side, and wherein the meniscus single-lens element fulfills conditional formula (1) below: −0.2<( R 1 −R 2)/( R 1 +R 2)<0.3 (1) where R 1 represents a radius of curvature of an object side surface of the meniscus single-lens element, and R 2 represents a radius of curvature of an image side surface of the meniscus single-lens element, and wherein the meniscus single-lens element fulfills conditional formula (2) below: 0.1 <tm/ts< 0.5 (2) where tm represents a core thickness of the meniscus single-lens element, and ts represents an axial thickness of the entire reduction optical system.