there is provided a multi - mirror - system for an illumination system , especially for lithography with wavelengths ≦ 193 nm . the system includes light rays traveling along a light oath from an object plane to an image plane , and an arc - shaped field in the image plane , whereby a radial direction in the middle of the arc - shaped field defines a scanning direction . the first mirror and the second mirror are arranged in the light path in such a position and having such a shape , that the edge sharpness of the arc - shaped field in the image plane is smaller than 5 mm in the scanning direction . furthermore , the light rays are impinging on the first mirror and the second mirror with incidence angles ≦ 30 ° or ≧ 60 ° relative to a surface normal of the first and second mirror .