Measurement of centering error of a lens with cyclic optical configuration

Abstract

A new technique for the measurement of centering error (CE) of a lens using a cyclic path optical configuration (CPOC) is presented. The test lens (TL) is placed in the CPOC, adjusted for zero lateral shear. The mechanical axis (MA) of the TL holder is prealigned along the direction of the central ray (CR) of the counterpropagating collimated beams of the CPOC. A pencil beam is also set along the CR outside the CPOC. If the TL is free from CE, then its optical axis (OA) would coincide with the MA and the CR. The focal points F1 and F2, formed by the TL, and the center of the Haidinger-type fringes, due to interference of the light from F1 and F2 (which is along the line joining F1 and F2), would also lie on the CR. In the presence of CE, F1 and F2 would be laterally displaced from the CR and the fringe center (FC) suffers a deviation from the CR. Adjustments in the angular and lateral positions of the TL necessary to align the OA along the CR, as can be ensured from the coincidence of the FC with the CR, give a measure of the CE.