Abstract: In the case of a lens system (1), in particular in the case of a projection lens system for semiconductor lithography, it is possible to exchange at least one optical element, in particular the final optical element in the beam direction in the form of an end plate (3). For adjusting the exchangeable optical element (3), an optical quality fit with a fitting surface (6) is set between the optical element (3) and a mount (5) or a part connected to a mount (5).

Abstract: An apparatus for adjusting devices and for setting adjustments, in particular in a &mgr;m range, nm range and below, in particular of optical elements in semiconductor lithography, comprising a base part and a head part spaced apart therefrom., the two parts being connected to one another by at least one adjustment device, and the adjustment device having side parts, the angle of which, or the spacing between which, can be adjusted or see by a length-adjustment device.