Optical system design for the 6.5m Southern Spectroscopic Survey Telescope and related multi-object fiber-fed spectrophotometer

The Southern Spectroscopic Survey Telescope (SSST) is a planned multi-wavelength sky survey telescope. The main scientific instrument of the telescope is an astronomical spectrometer. In this paper, we present a feasible optic system design based on wide-field Cassegrain corrector configuration for the telescope and related multi-object and fiber-fed spectrograph (MOFFS) system. The latest telescope design has a large field of view (FOV) of 2.6°×2.6° with its image spot size less than 0.3 arcsec in diameter for its full FOV in 80% encircled energy with the atmospheric dispersion effect taken into consideration. The MOFFS system based on the Volume Phase Holographic Gratings (VPHG) has an RMS radius of less than 12μm from center to edge of the fiber slit and the working band from 360nm to 1100nm while having the VPHG diameters less than 120mm. The camera group lens exhibited a transmittance higher than 88% at the whole working waveband.