Abstract: An interferometric instrument that includes a radiation generating unit for emitting briefly coherent radiation is used for sensing the surfaces of a test object by determining an interference maximum. Precise determination of the interference maximum, and therefore precise sensing of the test object, are achieved by providing, in the optical path of the first beam component and/or in the optical path of the second beam component, an arrangement which produces a frequency shift between the two interfering beam components and by providing a beam splitting arrangement, located in front of the photodetector arrangement in the optical path of the interfered radiation upstream from the photodetector device, which can be used to split the beams into at least two spectral components and supply them to the photodetector arrangement either directly or via additional elements on the photodetectors assigned to the components.