The aberrations of diffraction gratings are described without any restrictions on the symmetry of the substrate, the curvature of the grooves, or the position of the entrance slit. The description comprises second-order focusing conditions, including the generalization of the Rowland circle, and the conditions for astigmatism, length, slope, and curvature of the focal lines, comatic and fourth-order aberrations. Relations are shown between aberrations of second and higher orders. Applications to several types of mountings are included.
