Quote:
Originally Posted by Stefan Buda
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.
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I have often though about cooling my CDK actively. Any suggestions on how to do that? One way I thought of was a portable AC unit with one of those flexible tubes. I could direct it to the underside of the scope or perhaps flow it over the top of the scope so some would go down inside it or take the shroud off and blow at it sideways just above the mirrored section of the body.
Greg.