channels into the optical path of the illumination instrument for the setting adjustment for example there are a greater number of mirror facets on the second faceted mirror 5 than correspond to the number of mirror facets on the first faceted mirror 4 the mirror facets are not represented in fig1 for the sake of clarity as the object to be exposed there is a wafer 11 on a support unit 9 fig2 shows an individual mirror facet 12 with a mirror surface 15 which is formed by a cylindrical mirror facet head 13 and a cylindrical mirror facet base 14 in the exemplary embodiment the cylindrical mirror facet head 13 has a diameter of for example 20 mm and the cylindrical mirror facet base 14 has a diameter of about 8 mm the mirror facet 12 has an overall length of 60 mm for example for reasons of processing and thermal loading silicon is selected as the material of the mirror facet 12 the mirror facet 12 may of course be made of a stainless steel alloy or other materials which meet the requirements for polishability mechanical thermal and long term stability and ultrahigh vacuum compatibility uhv compatibility what is important when selecting the materials for the mirror facets 12 in particular is that the materials being used should have a high thermal conductivity so that the heat generated because of the beam power can be dissipated the mirror surface 15 of the mirror facet head 13 may be spherical.