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 degrees x2.6 degrees 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 12 mu m 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.