Abstract: An apparatus and method for measuring the surface contour of an aspheric optical surface 36. This is accomplished by splitting a single coherent beam of light into two individual beams with one beam tilted with respect to the other. The degree of tilt is adjusted until a single interference fringe is observed. This single fringe is then directed onto the aspheric surface 36 under test by means of a focusing lens 30. By the use of a beam spliter 24 the reflected fringe is then directed onto a multi-element optical detector 40 . The shape of the fringe reflected onto the detector 40 corresponds to the shape of the aspheric surface 36. A phase modulating mirror 26 is then moved to increase or decrease the path length of one of the two interfering beams of light. This results in sweeping the fringe across the entire aspheric surface 36 so that the entire aspheric surface 36 can be measured. The result is an easy to perform measurement of the aspheric surface 36 which is close to diffraction limited.