3.6.2 The Schmidt telescope
18.104.22.168 The basic principles of the Schmidt telescope. Bernhard Schmidt's publication in 1931 [3.31] represented the second revolutionary advance in the theory of telescope optics of this century. Schwarzschild had made the first such advance in 1905 [3.1] with his analysis of the possibilities of field correction by varying the aspheric forms of two mirrors with optical power as a function of the stop position. The bulk of the theory of § 3.2 derives from Schwarzschild's work. Schmidt's advance consisted of the systematic shift of the stop to the centre of curvature of a spherical primary, as discussed in § 3.6.1, combined with the insertion of an aspheric refracting corrector plate in the plane of the stop, as shown in Fig. 3.27. The Schmidt concept simply transfers the aspheric correction term from the Newton paraboloidal primary to the refracting corrector at its centre of curvature. Monochromatically, as we have seen in § 3.4, such a corrector plate with a fourth power figuring term
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