Subaperture testing of aspheres with annular zones

A subaperture configuration to test aspheric optical components or systems has been developed. The aperture is divided into annular subaperture regions, and an interferometer is refocused for each region to reduce the fringe density. The method is suited to phase-measuring interferometry and may be used with standard interferogram reduction software. The theoretical basis for the method, requirements for the number of annular zones, sensitivity to the selection of the number of polynomials, and tolerances for centration and radius are described. Numerical and experimental validations of the algorithm are described. The method may eliminate the need to use null lenses for measuring some aspheres at the center of curvature.