Investigation of optical distortion self-compensation ability in the MUltiplexed Survey Telescope

Abstract

MUltiplexed Survey Telescope (MUST) proposed by Tsinghua University aims to build a 6.5-meter widefield telescope for the ground-based spectroscopic survey. MUST adopts the Ritchey-Chretien system with the Cassegrain focus, consisting of an active support primary mirror, a passive support secondary mirror and a multiple-element widefield corrector. In order to fulfill the needs of the widefield spectroscopic survey, the primary mirror is supported in a specific approach rather than traditional methods, which results in optical distortions in the center region of the beam. In this paper, we presented a self-compensation method using the corrector itself to compensate the optical distortion caused by the primary mirror. Based on the optical system of MUST, an optical model of the self-compensation is established, and numerical simulation is conducted to implement the optimization of the corrector and investigate the self-compensation ability. Simulation results indicate that the surface shapes of the elements inside the corrector could be evolved to realize the self-compensation through the optimization of the widefield corrector, including the materials, surface shapes and load conditions. By using the presented self-compensation method, the optical distortions are well compensated and the image quality at the focal plane could be effectively improved.