Patent ID: 7603010

Claim:
An optical assembly for use in a lithography projection exposure apparatus, comprising: at least one optical element adjustable in at least n degrees of freedom, where n is between 2 and 6; at least one actuator for adjusting a position of the at least one optical element; and a plurality of encoder modules for sensing the position of the at least one optical element regarding the at least n degrees of freedom, wherein the plurality of encoder modules comprises at maximum n−1 encoder modules, wherein each encoder module of the plurality of encoder modules comprise a structured surface and a sensor head with a measuring direction, the structured surface comprises at least a structure according to a coordinate system selected from the group consisting of a Cartesian coordinate system, a polar coordinate system, and an inclined coordinate system, and wherein the structured surface is attached on the at least one optical element or is a part of the surface of the at least one optical element.