Quote:
Originally Posted by Satchmo
Just to clarify there the on the Adcock 12" mirror I tested for Seb . The main problem was the thermal inertia of a 2 1/8" thick mirror , and a minor zone out near the edge and there was no astigmatism. A thinner mirror will perform much better in real world conditions and as the seeing will effect high power viewing with a 30cm on more nights than a 20cm allowance must be made for the increase in aperture.
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Thanks for clearing that up and for doing the test Mark. Looks like the secondary would've been the culprit behind the astigmatism. The zones you've found in the primary and its struggle to cool would've contributed aswell.
Quote:
Originally Posted by Astroman
Congrats on the upgrades Sab... sounds like a nice scope your getting out of it....
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cheers Astroman, this'll be pretty much my dream scope... until I can afford a 30 incher with an observatory
Quote:
Originally Posted by JethroB76
Ah, yeah given it was an Adcock mirror, I thought maybe a move to a thinner mirror was behind the change. Was also making sure I hadn't missed it coming to grief in some way  |
Taking Mark's test results into consideration, and subsequently the likelyhood of the secondary introducing some astigmatism, I had to think long and hard.... could I live with some minor zones on the primary and just replace the secondary? I decided to replace both, as it was a good opportunity to go for a thinner primary while I'm at it, and for piece of mind that whenever the view is bad, it is for sure the seeing, not the optics.
While the scope is in Peter's shop, he not only did a few other minor jobs on it at my request, he also took it upon himself to replace the temp gauge with a new probe for the mirror and the SDM logo on the focuser board, as it became a little stained. Now that is service!
