The error caused by nonzero fringe pattern in a phase shifting interferometer is `harmful' to testing a long radius optic. In this paper, with the help of a concept of retrace error the error is analyzed through the combination of experiments with simulated calculations, and more sensitive elements are found in system alignment, so that the effect of the misalignment of optical elements on the retrace error is reduced to minimum.
Sen Han, Sen Han,
Erik Novak, Erik Novak,
"Retrace error for the measurement of a long-radius optic", Proc. SPIE 3749, 18th Congress of the International Commission for Optics, (19 July 1999); doi: 10.1117/12.354906; https://doi.org/10.1117/12.354906