Error compensation for mirror symmetry absolute test

A method is proposed to compensate intrinsic error in mirror symmetry absolute test. Because of the limitation of rotation times of flat A, intrinsic error of CNθ terms occurs in reconstructed wavefronts of flats A, B and C. If flat A is rotated to a new azimuthal position, and the wavefront difference between two measurements before and after rotation is calculated, the Zernike coefficients of CNθ terms can be obtained by solving coefficient equations due to rotation invariability of the form of Zernike polynomials in polar coordinates. Therefore, the intrinsic error of CNθ terms may be compensated. Because the amount of CNθ terms is infinite, the compensated terms are decided in terms of the balance between intrinsic error reduction and computational effort. Computer simulation proves the validity of the proposed method.