Projection optical system

Abstract

A projection optical system comprising a first lens having a positive refractive power, a second lens having a negative refractive power and a third lens having a positive refractive power, the lenses being arranged in ascending order in number from the side of an illuminated object, wherein when the optical system is regarded as an imaging optical system receiving a light beam from the side of the illuminated object, the effective focal length is represented by f, the total refractive power is represented by Pt=1/f, each lens surface of the three lenses are referred to as a first lens surface to a sixth lens surface from the side of the illuminated object, the refractive power is represented by Pt, the center thickness of the second lens is represented by L2 and f number is represented by F, the expressions 1.3 < P ⁢ 5 / Pt 0.1 < L ⁢ 2 / f < 0.25 F < 0.7

Dependencies are inferred from the claim text.