Patent ID: 7312463

Claim:
A catadioptric projection objective for imaging an off-axis object field arranged in an object surface of the projection objective onto an off-axis image field arranged in an image surface of the projection objective while creating at least one intermediate image comprising in that order along an optical axis: a front lens group having positive refractive power for converging radiation coming from the object field towards a mirror group entry of a mirror group; the mirror group having the object side mirror group entry, an image side mirror group exit, and a mirror group plane defined transversly to the optical axis and arranged geometrically between the mirror group entry and the mirror group exit; and a rear lens group with positive refractive power for focusing radiation emerging from the mirror group exit onto the image surface; the mirror group having: a first mirror for receiving radiation from the mirror group entry on a first reflecting area; a second mirror for receiving radiation reflected from the first mirror on a second reflecting area; a third mirror for receiving radiation reflected from the second mirror on a third reflecting area; and a fourth mirror for receiving radiation reflected from the third mirror on a fourth reflecting area and for reflecting the radiation to the mirror group exit; at least two of the mirrors being concave mirrors having a concave mirror surface having a surface of curvature rotationally symmetric to the optical axis; wherein: the mirrors of the mirror group are arranged such that at least one intermediate image is positioned inside the mirror group between mirror group entry and mirror group exit, and that radiation coming from the mirror group entry passes at least four times through the mirror group plane and is reflected at least twice at a concave mirror surface of the mirror group prior to exiting the mirror group at the mirror group exit; the mirror group entry is positioned in a region where radiation exiting the front lens group has an entry chief ray height; the second reflecting area is positioned in a region where radiation impinging on the second mirror has a second chief ray height deviating from the entry chief ray height in a first direction; and the fourth reflecting area is positioned in a region where radiation impinging on the fourth mirror has a fourth chief ray height deviating from the entry chief ray height in a second direction opposite to the first direction.