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Old 22-11-2013, 02:25 PM
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Satchmo (Mark)
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Join Date: Dec 2005
Location: Sydney
Posts: 1,858
Originally Posted by alpal View Post
Read it more closely.
The spot diagrams are still for a Newtonian without a coma corrector/ field flattener .

For example, Corrected DK's ( CDK's ) such as by Planewave are simple Dall- Kirkham Cass design with a corrector . Without the corrector they have the worst coma of any cassegrain design. With corrector they are beyond reproach .Comparing designs for imaging by looking at mirror systems without their correctors is just a waste of time. Even RC's require field flatteners which can be two lens involved.

The word 'astrogragh' implies a unified system designed to image the sky - lets stick to that definition.
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