The tilted relationship between the reference and test mirrors (24,26) of a Fizeau interferometer is used to spatially separate the reflections (R,T) from the two surfaces. The separate beams (R,T) are filtered through a spatial polarization element (32) that provides different states of polarization to the beams. The beams (R,T) are subsequently recombined to form a substantially collinear beam that is processed using a spatial-phase-shift interferometer (44) that permits quantitative phase measurement in a single video frame. Alternatively, two beams (104,106) with orthogonal polarization are injected into the Fizeau cavity (20) at different angles, such that after reflection from the reference and test optics (24,26) they are substantially collinear. Unwanted reflections are blocked at the focal plane through the use of a circular aperture (112). Short coherence length light and a delay line (84) may be used to mitigate stray reflections, reduce measurement integration times, and implement temporal phase averaging.