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Old 18-01-2020, 02:05 PM
glend (Glen)
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glend is offline
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,495
Originally Posted by Outcast View Post
In simple terms please, what is the difference between a classical cassegrain & a Richey Creighton design scope..

I understand the difference between these & say an SCT or Mak but, haven't been able to find out the main difference between the Classic Cat & an RC..

Not that I want one... I'll be dead if I buy anything else astro related...

Just curious in expanding my knowledge...
Well a couple of things: an RC is more of an imaging scope, it is faster at f8, but has a larger central obstruction (say 40%), the hyperbolic mirror set is designed to be coma free (well third order in theory, and free of spherical aberation).
The Cassegrain has a smaller central obstruction ( say 30%), and is slower at f12 (ie longer focal length, and not as concerned with coma at the edges.
The Cassegrain is the original folded design which the RC grew out of, in a sense.
That's my take on them, one RC is an astrograph design and the pure Cassegrain is visual mainly but can be used for planetary imaging.
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