Aspherical lenses are increasingly used in consumer products such as video cameras and compact disk pickups. It is that much work needs to be done for more effective manufacture of aspheical lenses, one area of which is the production line inspection of produced lenses. A lateral-shearing interferometry specially devised for production line inspection of lenses is presented. The interferomtry is configured with four square prisms whose relative sliding motions readily provide lateral-shearing and phase-shifting necessary for evaluating the beam wavefront collimated by the lens under test. The prisms are attached face-to-face by using immersion oil so that undesirable disturances from external mechanical vibration and atmospheric turbulence can be minimised in the measurement. Further, a special phase-measuring algorithm of least-squares is adopted to compensate the phase-shifting error caused by the thickness variation in the immersion oil holding the prisms. Measurement results proved that the interferometry has a repeatability of less than λ/100
