Patent ID: 8629972

Claim:
A projection objective for imaging an object field in an object plane into an image field in an image plane, the projection objective comprising: at least six mirrors of which at least one mirror has a freeform reflecting surface, wherein: the projection objective is a microlithography projection objective; the image plane is the first field plane of the projection objective downstream of the object plane; the projection objective has an overall length, T, which is a distance between the object plane and the image plane in a direction perpendicular to the object plane; a first point in the image plane is a projection in a direction perpendicular to the object plane of a central field point of the object field; during operation of the projection objective, a ray of light from the central field point of the object field intersects the image plane at a second point in the image plane; an object image shift, d OIS , is a distance between the first and second points in the image plane in a direction parallel to the image plane; and a ratio of T to d OIS is smaller than 5.