Study about distortion measurement of NFOV lens based on star point method

In order to measure the distortion of the narrow field of view (NFOV) lens by means of star point method, both star point center orientation and star size, affecting the accuracy of the distortion measurement, were studied. First of all, in order to improve the star positioning accuracy, Otsu algorithm and the barycenter calculation were combined to calculate the location of star point. At the same time, the calculated results were compared with the traditional centroid algorithm. Then, the effect of the star size on the stability of the star point positioning was analyzed in the experiments. Finally, the absolute and relative distortion of the lens was measured for the star points whose mean square error of coordinates is 1/71 pixel. The results show that the distortion of the NFOV lens can be measured with high precision and this method can meet space application.