Patent ID: 7274513

Claim:
Off-axis projection optics comprising: first and second mirrors positioned off-axis and sharing a confocal point that are arranged to reduce linear astigmatism, wherein a distance between an object plane and the first mirror is l 1 , an incident angle of light coming from the object plane to the first mirror is i 1 , a distance between the first mirror and the confocal point is l 1 ′, a distance between the confocal point and the second mirror is l 2 , an incident angle of light coming from the first mirror to the second mirror is i 2 , and a distance between the second mirror and an image plane is l 2 ′, the arrangement of the first and second mirrors satisfy the following l 1 ′ + l 1 l 1 ⁢ tan ⁢ ⁢ i 1 = l 2 ′ + l 2 l 2 ⁢ tan ⁢ ⁢ i 2 .