The <i>intensity of illumination</i> of the spectrum from a concave grating is computed. The customary arrangements are compared of which some correct the astigmatism of the spectral lines (sections 1–6). A cylindrical lens in front of the plate, as suggested by Humphreys and Gehrcke, seems to be the only device that increases the intensity without reducing dispersion and resolving power. Thus for a small spectral range a reduction of the time of exposure to 1/24 has been realized without any loss of resolving power (section 6). The bearings of the results on the spectra from the grating at grazing incidence (vacuum spectrograph), the plane grating and the prism are discussed (sections 7–9). The main results are checked by experiments.
O. OLDENBERG, "ON THE INTENSITY OF ILLUMINATION IN SPECTROGRAPHS," J. Opt. Soc. Am. 22, 441-452 (1932)