Study of matching methods for error evaluation of optical free-form surface

The matching methods between measuring surface and design surface were studied for the profile error evaluation of free-form surface. Based on the matching together of both center points and normal vectors of measuring surface and design surface, a pre-position method by five feature points including center point and four corner points was put forward to achieve better preliminary matching. The dual optimization method integrating the least square method and the least condition principle was presented for the accurate positioning. The results show that the matching accuracy can achieve the nanometer level. At last, an actual test of aspheric surface proves the validity of methods.