Optical design of off-axis astronomical space telescope based on freeform surfaces

摘要

A large-aperture, wide field-of-view, three-mirror optical system for a space borne astronomical survey telescope has been designed. The unobstructed optical system with a circular pupil has a 2 meter aperture, 1.7 deg~2 FOV, and provides remarkably good imagery. Freeform surfaces and decentered/tilt surfaces are introduced to the system, which have the advantage of balancing the unsymmetrical aberrations, especially for the wide-field off-axis optical systems. The evaluation of image quality is that the value of the RMS wavefront error is 21 nm , the ellipticity is less than 6.5% in the main imaging area (about 1.1 deg~2), and the maximum radius of Encircled Energy 80% (EE80) is less than 0.09arcsec.