Abstract: In a range finder for measuring absolute distances, a time partially coherent light source is provided. A beam emitted by it is split into a reference beam (B), which passes along a reference path, and a testing or measuring beam (A), which can be focused onto a testpiece (4). The radiation (A') reflected by the testpiece is brought to interference with the reference beam (B). In a position-sensitive detector array, the testing and reference beam are superimposed. The coherence of the two waves is directly determined from the intensity distribution on the detector array. The distance of the test-piece is calculated from the intensity distribution on the detector. Preferably, upstream of the detector array is connected an optical grating (6) with a grating spacing at least approximately corresponding to the spacing of the interference fringes on the detector array.