A Coudé Echelle Spectrograph with a Large Mosaic Grating but with Small Corrector Lenses
A spectrograph is described which uses a 30 cm by 60 cm mosaic echelle grating with 316 g/mm. The large free spectral region permits removal of overlapping orders with a filter or a small grism but is not suitable for the stacking of many orders. It is not a survey instrument. The camera mirror is made paraboloidal to avoid the need for large refractive correctors such as a Schmidt plate or a Maksutov lens. Instead, a small triplet lens is located near the focus, and can be made of fused silica at low cost to permit good transmission in the ultraviolet down to the atmospheric cut-off. The collimator mirror is spherical.
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