Patent ID: 6259508
Filing Date: 2001-07-10
Classification: G03F

Abstract:
A projection optical system capable of forming an image of an object, comprising, objectwise to imagewise, along an optical axis:a) a first lens group having positive refractive power;b) a second lens group having negative refractive power;c) a third lens group having positive refractive power;d) a fourth lens group having negative refractive power and a first aspherical surface;e) a fifth lens group having positive refractive power and an aperture stop;f) wherein the projection optical system is designed such that paraxial rays travelling parallel to the optical axis imagewise to objectwise intersect the optical axis at a location Q between said fourth lens group and said fifth lens group;g) at least one of said fourth and fifth lens groups includes a second aspherical surface arranged between said first aspherical surface and said aperture stop;h) said fifth lens group includes a third aspherical surface arranged imagewise of said aperture stop; andi) wherein the following condition is satisfied:0.01<d.sub.Q /{L.times.(1-NA)}<0.4 (1)wherein the image and the object are separated by a distance L, said location Q and said aperture stop are separated by a distance d.sub.Q, and NA is an imagewise numerical aperture of the projection optical system.