Evaluation of fringe pattern magnification for lens dioptric power measurement

Dioptric power measurement is an essential part of the characterization and quality control of lens manufacturing. In this framework, a fairly simple and potentially cost-effective method for lens characterization by interferometric fringe evaluation is reported. This technique consists of acquiring images of straight and parallel fringes projected onto a planar screen through the lens to be tested and in the regions surrounding the lens. Upon phase evaluation procedures, two apparent three-dimensional shapes of the screen are obtained, namely, the background contour and the one visualized through the test lens. The lens power is obtained as a function of the ratio between the two shapes and the parameters of the optical setup. The fringe pattern evaluation was performed by four-stepping and phase unwrapping methods. The results obtained by this technique were compared with the ones obtained by a commercial focimeter in the measurement of unifocal and progressive power lenses.