Echelle/Grism Spectrograph

More even spectral dispersion over detector area makes all wavelengths more distinguishable. Proposed echelle spectrograph includes grating/prism combination, called "grism," to make spectral dispersion over detector more even than usually in such instruments. Instrument performance improved, with little additional manufacturing effort. Furthermore, since grism placed within collimated light and its faces are optically flat, introduces no aberrations into optical system.