Optical design of the long slit spectrograph for 1m telescope

In this article we describe optical design of a long-slit spectrograph for the 1-m telescopes of the Special Astrophysical Observatory of Russian Academy of Science and Bonhyunsan Optical Astronomical Observatory (Rep. of Korea). The operating spectral range is 350-750 nm. The spectrograph is to provide several observing modes including the following spectral resolutions: R100; R1000; R4000. It provides the direct imaging regime as well. The spectroscopic and imaging regimes are constrained with the use of a 2k × 4k CCD detector of 13.5 μm pixel size. For dispersing optical elements we use volume-phased grisms at each of the spectroscopic modes. The highest resolution mode (R4000) is provided by consecutive observations in three spectral ranges: 350-450 nm; 450-580 nm; 580-750 nm. Light losses in the spectrograph are achieved to be less than 50% in the whole spectral range due to the use of Ohara glasses. As to technical advantages of the presented solution we would notice its ability to provide all observing modes in a wide spectral range with one, non-replaceable projection camera without glued lenses. The spot diagram size does not exceed 2 pixels size in all modes and wavelengths.