Fig. 9.5. Wynne triplet corrector for prime focus of paraboloidal primary. See the article by
Wynne (1974) for characteristics of the lens elements for an//3.25 primary.
9.3.
CASSEGRAIN FOCUS CORRECTORS
Of the common two-mirror telescopes discussed in Chapter 6, the Ritchey-
Chretien t3^e has the largest field at the Cassegrain focus. To third order, the only
significant aberrations are astigmatism and field curvature. It was first shown by
Gascoigne that the placement of an aspheric plate in the Cassegrain beam
removes the astigmatism without introducing a significant amount of coma and
spherical aberration ...
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