Measurement apparatus, method for measuring by interferometry, processing method, optical element and lithography system

Measurement apparatus for measuring a shape of a surface of a test object by interferometry, comprising:

• an illumination device comprising an illumination source configured to generate an illumination wave,
• an interferometer device comprising a splitting element configured to split the illumination wave into a test wave, which is directed at the surface and returned as a returning test wave, and into a reference wave, and to combine the returning test wave, which has interacted with the surface being measured, with the reference wave,
• a registration device configured to register an interference pattern and evaluate the interference pattern to determine a deviation of the shape of the surface being measured from a target shape,
• a control device configured to split the surface being measured into a plurality of individual areas being measured, and
• a positioning device configured to position the test wave on the surface being measured such that the individual areas are respectively fully illuminated, wherein:
• the registration device is configured to determine, based on data from the individual areas, a deviation of the shape of at least a part of the surface being measured from the target shape, and
• the illumination device further comprises at least one adjustable stop device configured to define a subaperture of the interferometer device and to adapt the subaperture to the respective individual areas being measured.