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It's almost impossible to generalise. There are many designs that all go under the name of either Schmidt-Cass (SC) or Maksutov-Cass (MC). Are all surfaces of the MC spherical or not? Is the secondary of the MC a silvered part of the meniscus corrector or a separate mirror placed between meniscus and objective mirror? etc etc.
The original Schmidt camera was designed to work with a spherical primary and was coma free, but this makes the focal point is inaccessible for visual use, so compromises have to be made, which introduce some coma and astigmatism. Different designs make different compromises.
If you can lay your hands on it, there is a great book by Rutten and Venrooij called "Telescope Optics-a comprehensive manual for amateur astronomers" which describes just about every type of telescope design. ($69 at Bintel)
Geoff
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