Spectroscopy

Now consider putting a grating or grism in the collimated beam to do spectroscopy. The important choice for spectroscopy is the lines/mm of the grating, call this $M_{grating}$, which governs the spectral resolution. Typical numbers for large astronomical gratings range from 100-1200 lines/mm (apart from echelle gratings, which are used at a different rangle of incident angles and in more complex spectrographs).