Patent ID: 6459534
Filing Date: 2002-10-01
Classification: G02B,G03F

Abstract:
A projection optical system for projecting an image of an object onto an image plane, said projection optical system comprising:a plurality of lens groups including a positive lens group having a positive refractive power and a negative lens group having a negative refractive power, wherein, when a conjugate length of said projection optical system is L and the total power of the negative lens group or groups is &phgr;0, a relation 70>|LÃ—&phgr;0|>17 â€ƒis satisfied, wherein &phgr;0=&Sgr;&phgr;0i, where &phgr;0i is the power of the i-th negative lens group, wherein, when a height of an axial marginal light ray is h and a height of a most abaxial chief ray is hb, at least two surfaces which satisfy a relation 15>|hb/h|>0.35 â€ƒare aspherical surfaces, wherein, when an aspherical amount of an aspherical surface is &Dgr;ASPH, said at least two aspherical surfaces satisfy a relation 0.02>|&Dgr;ASPH/L|>1.0Ã—10âˆ’5 â€ƒand they include two aspherical surfaces having regions in which, from a center of the surface to a periphery thereof, their local curvature powers change with opposite signs, and wherein at least one of said at least two aspherical surfaces comprises one surface of an aspherical surface lens having one face defined by an aspherical surface and another face defined by a flat surface.