In the course of a systematic analysis of various design philosophies aimed at achieving high optical throughput low resolution spectrometers for telescopes in the range of 2-4 meters, two distinct optical designs were established. The first is optimised for a telescope prime focus having a fast F/ratio, and is based on a concave grating whose aberrations are corrected by 2 or 3 off-axis lenses. The second system is a focal reducer, utilizing lenses and transmission gratings only. The use of a particular glass type having an extremely low dispersion permits excellent correction of various aberrations over a wide spectral range. Both designs provide a two-dimensionally corrected field typical of present day CCD array formats. These designs are highly suitable for long slit or field spectroscopy and offer the possibility of rapid switching to direct imaging mode.
"Two Design Approaches For High Efficiency Low Resolution Spectroscopy", Proc. SPIE 0445, Instrumentation in Astronomy V, (9 January 1984); doi: 10.1117/12.966186; https://doi.org/10.1117/12.966186