The Ebert-type mounting is modified for use as a multiorder spectrograph, by replacing the spherical primary mirror of the Ebert with a paraboloidal mirror to eliminate the astigmatism and spherical aberration of the Ebert mounting, and by replacing the Ebert's rotating plane grating, normally blazed for use in the first order, with a fixed low-blaze-angle grating blazed at a longer wavelength such that the radiation at the shorter wavelengths, for which the grating will be used, will be most efficiently dispersed into a multiplicity of higher spectral orders. In a preferred embodiment of this invention, these spectral orders are separated using a twice-through cross-dispersing prism mounted near the grating surface, with the grating and prism mounted and aligned together in a crossed-dispersion assembly that is interchangeable with other crossed-dispersion assemblies containing other grating and prism combinations.