Concave aspheric test combining Dall with Offner null compensation using a plane wave.

A plane wave aspheric surfaces test is simpler and easier to assemble than a spherical wave test. An optical system combining Dall with Offner null compensation using a plane wave is proposed for measuring large-aperture and large-relative-aperture aspheric concave surfaces. One back compensation lens and one front compensation lens are used in the system, which can realize a high-precision null test. Based on the third-order aberration theory, the normalized theoretical parameters are calculated by formula derivation, and then are optimized after analysis. The design characteristic is compared with the classical plane wave Offner null test. A prototype experiment of the proposed method is carried out with a parabolic mirror of 500 mm diameter, at relative aperture 1/1, showing that RMS surface error of /40 can be obtained.