Quote:
Originally Posted by gregbradley
Its hard to imagine though an SCT outperforming a Planewave CDK. The secondary is not 50% like a lot of astrographs are. The exact % I am not sure of but I think its around the 40's.
Greg.
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According to what I said in my previous post a C14 with good optics should outperform your CDK.
It is hard to convince non-planetary imagers of the importance of thermal control. Your CDK's secondary assembly has a lot more mass (= thermal inertia = chimney effect), not to mention the large spider vanes acting as heat exchangers.
My 16" UDK ( U for uncorrected :-) ) has less than 25% obstruction and only two optical surfaces that can be tested very accurately. And yet I was not able to push it to its limit for a few years because the passive cooling arrangement I used initially, was creating a slightly asymmetric thermal gradient within the primary making it astigmatic. The problem was hard to detect because it produced a wave front error of about 1/4 lambda.
It took a Roddier test to identify the problem.
And to answer your initial question: Like other people have suggested, a large Newtonian is the way to go.