Near-null compensator, surface shape measuring instrument and measuring method for stitching measurement of aspheric surfaces sub-apertures

A near-null compensator for stitching measurement of aspheric surface sub-apertures mainly consists of a pair of CGH (computer-generated hologram) phase plates rotatable in opposite directions, the phase function of the phase plates consists of Z5 term and Z7 term of Zemike polynomial, the coefficients of Z5 and Z7 polynomials of the two phase plates are opposite numbers, and values of the coefficients are determined by the aberrations of off-axis sub-apertures; the phase plates are mounted on a pair of hollow precise turntables rotatable in opposite directions, and the optical axes of the phase plates are coincident with the rotation axes of the hollow precise turntables. The present invention further provides a surface shape measuring instrument for stitching measurement of aspheric surface sub-apertures comprising the near-null compensator. In addition, a method for stitching measurement of aspheric surface sub-apertures using the surface shape measuring instrument is also provided. The present invention has the advantages of simplified structure, compact space, low cost, high precision and adaptability, and the like.