The disclosure is directed to focusing one or more detectors of an interferometry system. An initial focus position may be determined by focusing a detector on an edge of a sample by comparing image contrast of intensity frames collected by the detector. Data associated with an inner edge of a ring formed by the image of the sample reflected on a reference flat may be collected from one or more positions near the initial focus position. The detector can be focused to a selected position by comparing edge data collected at the various detector positions near the initial focus position.