LAMOST multi-object spectrographs with asperized gratings

LAMOST is a powerful spectra survey telescope with 4 meter aperture and 5 degree FOV. Its focal plate with 1.75 meter diameter can accommodate 4000 fibers in which feeds 16 multi-object spectrographs. In the last conference of astronomical telescope and instrumentation hold in Munich, Germany in April, 2000, preliminary design for LAMOST multi-object spectrographs based on plane reflective gratings and Schmidt camera with refractive corrector has been reported. Here, use aspherized reflective grating instead of the plane reflective grating and need for refractive corrector plate is avoided. Compared to previous design using a refractive plate for correcting aberrations from both collimator and camera mirror, use of aspherized grating has the achromaticity advantage as well as less asphericity, and minimizes the number of optical surface. This would improve the efficiency of spectrograph and allows much broader spectral coverage. In this paper, we present the current design of multi-object spectrographs for LAMOST project.