Collector with fastening devices for fastening mirror shells

There is provided a projection exposure system operable in a scanning mode along a scanning direction. The projection exposure system includes a collector that receives light having a wavelength ≦193 nm and illuminates a region in a plane. The plane is defined by a local coordinate system having a y-direction parallel to the scanning direction and an x-direction perpendicular to the scanning direction. The collector includes (a) a first mirror shell, (b) a second mirror shell within the first mirror shell, and (c) a fastening device for fastening the first and second mirror shells. The mirror shells are substantially rotational symmetric about a common rotational axis. The fastening device has a support spoke that extends in a radial direction of the mirror shells, and the support spoke, when projected into the plane, yields a projection that is non-parallel to the y-direction.