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CFHT f/4 coude echelle spectrograph, 316-g/mm 30-cm mosaic grating

The optical design of an f/4 coude echelle spectrograph for the 3.6-m Canada-France-Hawaii Telescope is described and illustrated with drawings and diagrams. The basic configuration comprises a tilted spherical f/20 collimator mirror, a 30-cm 316-g/mm grating near the slit, a paraboloid camera mirror, and a small triplet corrector lens. Two sets of optics are provided, coated for optimal performance in the UV-blue and green-IR regions, respectively, and small remotely selectable variable-wedge grism or grens modules are located in the diverging beam from the slit to the collimator to prevent other orders from overlapping the part of the spectrum being recorded. Consideration is given to the Hartmann mask system, the mosaic grating controls, the collimator and camera mirror turrets, and the detector support.