Patent ID: 7706075

Claim:
A projection optical system which projects an image on a first object plane onto a second object plane, comprising at least four optical members which are arrayed in turn from the second object plane, and made of an isotropic crystal, wherein said at least four optical members are formed by alternately arraying optical members in each of which a <1 1 1> crystal axis is oriented along a direction of an optical axis, and optical members in each of which a <1 0 0> crystal axis is oriented along the direction of the optical axis, when said at least four optical members are determined as a first optical member, a second optical member, a third optical member, and a fourth optical member in turn from the first object plane, maximum angles θ 1 , θ 2 , θ 3 , and θ 4 between the optical axis and a light beam which propagates through said first optical member, said second optical member, said third optical member, and said fourth optical member satisfy: |θ i−θj|< 5°( i, j= 1, 2, 3, 4) and a curvature radius R 1 of a surface of said first optical member on a side of the first object plane, a curvature radius R 2 of a surface of said second optical member on the side of the first object plane, a curvature radius R 3 of a surface of said third optical member on the side of the first object plane, and a curvature radius R 4 of a surface of said fourth optical member on the side of the first object plane satisfy: R1<R2<R3<R4.