Distribution of PSF of The Near Earth Object Survey Telescope

The CCD field of view of the Near Earth Object Survey Telescope (NEOST) is 1.94°xl.94°. As a wide-field telescope, the focusing based on a single star will lead to an uneven distribution of PSF (Point Spread Function) on the CCD image due to the field curvature. The features of the PSF distribution on the CCD image are studied. By fitting the relation between the defocusing and the FWHM (Full Width at Half Maximum) of PSF, the curved focal surface is simulated and therefore the best imaging plane is determined. Hereby, a focusing method based on the optimum imaging plane determined by judging the histogram of FWHM is proposed.