Fig. 3.33. Spot-diagrams for the ESO 1 m, f/3.0 Schmidt telescope with the achromatic (doublet) corrector plate (glasses UBK7 and LLF6). Optimum curved field of radius 3050.5 mm and ±3.20° field for 24 cm x 24 cm plates (format identical with Fig. 3.29, but scale five times larger)

convex form is sufficient to compensate for the negative first order chromatic aberration generated by the pure Bouwers meniscus, which has slight negative power.

Excellent treatments of the basic theory are given by Bahner [3.5] and Schroeder [3.22]. Essentially, the following formulation is similar to that of Schroeder following Bouwers [3.32] and Maksutov [3.38]. A general analytical solution for the third order spherical aberration introduced by the thick concentric meniscus of the Bouwers telescope is possible, but complex. Bouwers himself simplified the formulation by assuming the approximation of a thin lens for an object at infinity. He starts from the formula [3.32], valid for the third order aberration of low power (1/f'men) and strongly "bent" lenses, for the angular aberration6. In our notation, the angular diameter of the aberration is

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