the maximum angle of incidence occurs at the right hand edge of mirror m 5 according to fig4 and amounts to approximately 22 u00b0 likewise the image plane 10 is the first field plane downstream of the object plane 5 a in the projection optics 9 likewise at least one of the mirrors m 1 to m 6 is a biconical freeform reflection surface in the projection optics 9 at least one of the mirrors m 1 to m 6 has a reflection surface that is a biconical freeform reflection surface which may be described by the following formula in this formula x and y denote the coordinates on the reflection surface in relation to a coordinate origin which is defined as the point of penetration of a normal through the reflection surface in theory this point of penetration may also be located beyond the used reflection surface z denotes the sag of the freeform reflection surface the coefficients cvx and cvy describe the curvatures of the freeform reflection surfaces along an xz and a yz section the coefficients ccx and ccy are conical parameters the freeform surface formula includes a leading biconical term and a subsequent xy polynominal with a coefficient a ji the following tables specify arrangement and shape of the optical surfaces of the mirrors m 1 to m 6 within.