Electromagnetic illumination radiation is produced and provided as an input wave. The input wave passes through a diffractive optical element and leaves as an incoming measuring wave, the wave front of the input wave being transformed such that the wave front of the incoming measuring wave is adapted to the desired shape of the effective reflection surface. Furthermore, the test object is disposed in a test position in which the incoming measuring wave is reflected back to the diffractive optical element as a reflected measuring wave, the reflected measuring wave passing through the diffractive optical element and leaving as an outgoing measuring wave, the propagation direction of the outgoing measuring wave being deviated in relation to the opposite propagation direction of the input wave. A reference wave branched off from the illumination radiation interferes with the outgoing measuring wave this interference being recorded by detector.