Patent ID: 7301694

Claim:
An off-axis projection optical system comprising: first and second mirrors that are off-axially arranged, the first mirror being a convex mirror and the second mirror being a concave mirror, wherein if a tangential and sagittal radii of curvature of the first mirror are R 1t and R 1s , respectively; a tangential and sagittal radii of curvature of the second mirror are R 2t and R 2s , respectively; an incident angle of a beam from an object point to the first mirror is i 1 ; and an incident angle of the beam reflected from the first mirror to the second mirror is i 2 , the following is satisfied: R 1t cos i 1 =R 2t cos i 2 R 1s =R 1t cos 2 i 1 R 2s =R 2t cos 2 i 2 .