The Luminosity of Spectrometers with Prisms, Gratings, or Fabry-Perot Etalons

Formulas have been established which express the flux given by a spectrometer as a function of the effective resolving power and of the dimension of the dispersive system (area of the base of the prism, or area of the grating, or area of the plates of the étalon). It is thus possible to compare the luminosities of the three types of instruments with, in each case, equal resolving power and equal dimension. This comparison reveals a great superiority of the grating over the prism for all regions of wavelengths, and a great superiority of the étalon over the grating. In the case of the étalon, the overlapping may be overcome by the use of several étalons in series.