Patent ID: 7486439

Claim:
A projection optical system for projecting a pattern on an object surface onto an image surface in a reduced size, said projection optical system comprising six reflective surfaces that include, in order of reflecting light from the object surface, a first concave reflective surface, a second convex reflective surface, a third convex reflective surface, a fourth concave reflective surface, a fifth convex reflective surface and a sixth concave reflective surface, wherein said projection optical system forms an intermediate image of the pattern, wherein the six reflective surfaces are arranged so that radii of curvature of these six reflective surfaces are substantially aligned with a certain optical axis, wherein a surface apex is defined, with respect to each of the six reflective surfaces, as one of nodal points between an optical axis and an approximately spherical surface, which one is closest to a reflection point of the light on each of the six reflective surfaces, the approximately spherical surface having a center that is defined as a center of curvature of each of the six reflective surfaces, and a radius that is defined as a radius of curvature of each of the six reflective surfaces, and wherein the following condition is met, where L 1 is an interval between the object surface and the surface apex that is the closest to the object surface, and L 2 is an interval between the surface apex of the first reflective surface and the surface apex that is the closest to the object surface: 0.75 < L ⁢ ⁢ 1 L ⁢ ⁢ 2 < 1.25 wherein a maximum incident angle at each point on a nodal line has an extreme in a region between Lmin+0.3×(Lmax−Lmin) and Lmax on the nodal line, the nodal line being formed between a light incident area upon which the light from an arc illuminated area on the object surface is incident, and a plane that includes a center point of a chord of the arc illuminated area shape on the object surface and an optical axis, the light incident area being located on one of the six reflective surfaces, which one has the largest maximum value of a light incident angle, where Lmin is a minimum value of a distance from the optical axis to each point on the nodal line, and Lmax is a maximum value of the distance from the optical axis to each point on the nodal line.