Billed as
aplanatic Schmidt telescopes, this series of 8-, 9Y4-, 11-, and 14-inch tube assemblies incorporates a 2-element field flattener and coma corrector in the main light-baffle tube that promises to correct distortions to the edge of the largest CCD detectors on the market.
In fact, one of the designs discussed there is an
aplanatic (coma-free) SCT virtually indistinguishable from what Meade is marketing as an "Advanced Ritchey-Chretien." Meade should call it an Advanced Schmidt-Cassegrain design instead.
Collaborating with French optical designer Henri Chretien, Ritchey showed that a Cassegrain-style reflector with two approximately hyperboloidal mirrors would be
aplanatic (free of coma) and thus able to cover large photographic plates from corner to corner with beautifully round stars.
Optics won, and we unscrewed the machined lens cap to reveal the
aplanatic, three-element objective, which has a central element made of ED glass.
It is an
aplanatic design (with the flint element a meniscus lens), which yields better spherical correction and reduced coma compared with designs that use a plano-concave flint element.