Field Lens And

Fig. 4.20 Optical design of LAMOST spectrographs for R = 2,000. This uses aspherized reflective gratings of 200 mm groove length and an aperture ratio of f/1.5 in this direction. A dichroic provides the two spectral ranges XX [370-590nm] and XX [570-900 nm]. The CCD detectors have 2048 x 2048 pixels of 24 x 24 ^m. The mounting angle between the collimator and camera axes is 80 = 35°. The normal diffraction angle, fi ~ 0, allows a design with axisymmetric aspherized gratings (Zhu and Lemaitre [97])

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