9 January 1984 Optical Design Of The All-Reflecting Coude Spectrograph Of The Canada-France-Hawaii Telescope
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Abstract
Two spectrographs were planned for the coude focus of the CFHT, the first having a F/7.4 camera and a large (76cm) plateholder, the second having a faster camera, F/3.7, and a smaller focal surface. The F/7.4 spectrograph began operation in 1981 and its optical design, including proposed additions, is described. It consists simply of a turreted hyperboloidal collimator mirror which illuminates a choice of 30x40cm gratings followed by a spherical camera mirror. When required, a small, high reflectance, diagonal mirror is added to direct light to a CCD or other electronic detectors. High transmission is possible because the spectrograph has few elements, some of which can have high reflectance coatings, and because it is designed for use with image slicers with which it is equipped. The image slicer used with the CCD has five slices and increases the width of the projected entrance aperture on the sky to that of the slit of a F/1.5 spectrograph, i.e.,(7.4)/5. (The gain of an image slicer comes from changing the shape of the entrance aperture whose area is the same as that of the portion of an ordinary slit illuminated by starlight by "trailing".)
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E H Richardson, E H Richardson, } "Optical Design Of The All-Reflecting Coude Spectrograph Of The Canada-France-Hawaii Telescope", Proc. SPIE 0445, Instrumentation in Astronomy V, (9 January 1984); doi: 10.1117/12.966187; https://doi.org/10.1117/12.966187
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