Patent ID: 7312851

Claim:
A reflective projection optical system by which an image of a first plane is formed at a second plane in a predetermined region spaced from an optical axis, comprising: an aperture stop for defining a numerical aperture of the projection optical system, wherein the aperture stop is provided with an aperture portion in which dimensions in two directions perpendicular to each other are different from each other, and wherein: when a plurality of image points on the predetermined region at the second plane are A 1 , A 2 , A 3 , . . . , An; the plurality of image points are sampled a plurality of times at substantially the same interval on the predetermined region at the second plane; an arbitrary one among the plurality of image points is Ai; two coordinate axes x, y perpendicular to each other on a plane parallel to a plane including the aperture stop are assumed; on the aperture stop periphery, a point at which the coordinate x is at a maximum is Pxu, a point at which the coordinate x is at a minimum is Pxb, a point at which the coordinate y is at a maximum is Pyu, and a point at which the coordinate y is at a minimum is Pyb; a spherical surface Si of a radius 1 about the image point Ad is assumed; coordinates at which light passing through the point Pxu and reaching the image point Ad crosses the spherical surface Si are (Xixu, Yixu); coordinates at which light passing through the point Pxb and reaching the image point Ai crosses the spherical surface Si are (Xixb, Yixb); coordinates at which light passing through the point Pyu and reaching the image point Ai crosses the spherical surface Si are (Xiyu, Yiyu); coordinates at which light passing through the point Pyb and reaching the image point Ai crosses the spherical surface Si are (Xiyb, Yiyb); and two variables NAxi and NAyi corresponding to the image point Ai are established, respectively, as follows: NAxi =( Xixu−Xixb )/2 NAyi =( Yiyu−Yiyb )/2, a predetermined shape of the aperture portion substantially satisfies {ΣNAxi (i=1˜n)}/n={ΣNAyi (i=1˜n)}/n.