Abstract

As an example of a mounting in which the optical components are not on the Rowland cylinder, the Seya-Namioka mounting is treated mainly from the standpoint of physical optics. An ambiguity in the physical meaning of Beutler’s focal conditions is clarified; using the corrected condition a brief summary of the optical conditions in this mounting is given. Astigmatism, spectral line shape, instrumental resolving power, and optimum grating width are discussed in detail and, for convenience of practical application, numerical results are also given for the following conditions: 1-m concave grating with 15 000 lines/in., first order spectrum, with ratios of the radius of curvature of the grating to the distances between the grating center and the entrance and exit slits 1.2223, and 1.2230, respectively, and the angle between the lines connecting the grating center to the entrance and exit slit 70° 15′.