Patent ID: 7177076

Claim:
A projection objective that provides a light path for a light bundle from an object field in an object plane to an image field in an image plane, said projection objective comprising: a first mirror; a second mirror; a third mirror; a fourth mirror; a fifth mirror; a sixth mirror; a seventh mirror; and an eighth mirror, wherein said light path is provided via said eight mirrors and is free of obscuration, wherein said light bundle includes light with a wavelength in a range of 10–30 nm, wherein said object field represents a segment of a ring field with an axis of symmetry that is perpendicular to an optical axis, wherein said light bundle has a chief ray of a field point that lies on an axis of symmetry and in a center of said object field, wherein said projection objective has therein a right-handed coordinate system with an x axis, a y axis and a z axis, wherein said z axis runs parallel to said optical axis and said z axis points from said object field to said image field, wherein said y axis runs parallel to said axis of symmetry and said y axis points from said optical axis to said object field, wherein for each of said eight mirrors i (i=1 to 8) there is a characteristic quantity C i , which is defined as a scalar product of a unit vector x in a direction of said x axis and a vector product between one unit vector n i before , which has a direction of said chief ray striking an ith mirror, and a unit vector n i after , which has a direction of said chief ray reflected at said ith mirror, thus C i =x(n i before ×n i after ), wherein C 1 >0 applies to said first mirror, wherein C 2 <0 applies to said second mirror, wherein C 5 <0 applies to said fifth mirror, and wherein C 6 >0 applies to said sixth mirror.