The method of null test is widely used for testing an aspheric mirror. During optical manufacturing process, the mirror has to be moved up and down for testing and fabricating. Because the alignment of null test is difficult and time costing, the efficiency of making aspheric mirror is decreased greatly. In order to solve the problem, we developed a software based on polynomial fitting to calculate the misalignment parameters. By using the software and computer numeric controlled adjusting equipments, the efficiency of testing is increased and the accuracy of test has reached up to λ/40 RMS where λ equals to 632.8nm, which has fulfilled the demand of the designer.
The characteristics and effects of alignment error on test results are analysed in this paper. The mathematical model are established, the least square method is used to determine the misalignment. Procedures are presented that allow for separation of misalignment from misfigure in asphere testing. The misalignment-induced aberrations by corrector and the support of the mirror can be calculated and subtracted from segment interferogram so that only true misfigure remains. The accuracy of the system can reach up to 0.028λ(λ=632.8nm).