REFLECTIVE GRATING INTERFEROMETER FOR MEASURING THE FOCAL LENGTH OF ALENS BY DIGITAL MOIRE EFFECT

A new technique is proposed, based on digital moire effects,for measur ing the focal length of a lens. The test lens is illuminated by a vari able pitch interference pattern produced by an interferometer which ma kes use of a reflective diffraction grating, Moire fringes are generat ed by digitally adding the magnified images produced by the lens on th e original interference pattern. The focal length of the lens can be d etermined by counting the number of moire fringes. This technique is s uitable for measuring both long and short focal length lenses. The foc al lengths of both positive and negative lenses were experimentally me asured.