With the intention of precision measurement of aspherical lenses and aspheric surfaces, the Ronchi test is revisited to devise a special scheme of multiple-beam lateral shearing interferometry. A holographic sinusoidal grating is used instead of conventional binary gratings so that only 0 and ±1 order diffraction beams induce necessary lateral shear with high quality. In addition, relative fringe phases of wavefront slopes are automatically obtained by applying phase shifts in sheared interferograms. At this time, as the grating was located obliquely in a transverse plane, we can make a phase shift of the same direction about a variety of oblique angle with the grating. Finally an elaborate in-line calibration scheme is incorporated to identify the system scale factors with which the three-dimensional profiles of test surfaces are accurately reconstructed from the measured wavefront slopes. In conclusion, experimental results prove that the proposed technique is useful especially for aspheric surfaces with a short focal length.
