A novel variation of Michelson's interferometer uses tilt- and shear-compensation optics to allow various mirror motions to produce variation of path difference. The tilt-compensation mechanism consists of two complementary reflections from a single plane mirror to produce a beam having a constant angle of propagation, typically the same as the input beam. Using a retroreflector to invert the image of the single plane mirror before the second reflection produces the complementary reflections. A particularly efficient embodiment of the present invention uses a balanced disk-shaped mirror to effect very rapid variation of path difference by nutation or precession. Other advantages of tilt-compensation include photometric stability. This interferometer has applications in spectrometry, spectral imaging and metrology.