Optimized optical system with a 1.65  m wide-field corrector for the 6.5  m high-performance MUltiplexed Survey Telescope.

The development of modern large-scale spectroscopic survey telescopes responds to the urgent demand for spectral information in astronomical research. Tsinghua University has previously proposed a 6.5 m MUltiplexed Survey Telescope consisting of a Ritchey-Chretien configuration and a 1.8 m multi-element wide-field corrector, achieving excellent performance and world-leading survey efficiency. However, an optimized 1.65 m multi-element corrector with five lenses is proposed to overcome the constraints on glass uniformity and verification in fabrication of the previous corrector design. It maintains outstanding image quality, with the 80% enclosed energy diameter not more than 0.559 arcsec within 3° FoV over up to a 55° zenith angle. The optimized optical system does not revise the working mode of the ADC or the curvature of the primary mirror while ensuring the reasonability and accuracy of manufacturing of large corrector elements. It provides a more feasible reference optical design for the MUltiplexed Survey Telescope in subsequent iterations and communications with manufacturers.