Patent ID: 7995884

Claim:
An optical assembly, comprising: at least one optical element adjustable in at least n degrees of freedom, wherein n is between 2 and 6; at least one actuator configured to adjust a position of the at least one optical element; and a plurality of encoder modules configured to sense a 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; at least one of the plurality of encoder modules is configured to sense the position of the at least one optical element in at least two degrees of freedom; each of the plurality of encoder modules comprises a structured surface and a sensor head with a measuring direction, the structured surface comprises at least a structure configured to provide information on a relative position between the sensor head and the structured surface; a member is associated with the at least one optical element; the member is selected from the group consisting of a reading head and the structured surface; and the optical assembly is configured to be used in a lithography projection exposure apparatus.