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Old 02-02-2018, 08:57 PM
Stefan Buda
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Stefan Buda is offline
Join Date: Jul 2013
Location: Melbourne, VIC
Posts: 441
Originally Posted by multiweb View Post
That moon shot looks good. Very close to the finished product now.
Thanks Mark, and you are absolutely right about being close with the optics: With Bratislav's help, I did a couple more Roddier tests and it turns out that no figuring is required.
The first one was done a few days ago and the only change from the last posted Roddier test is that I rotated the Mangin about 90 degrees. Interestingly the orientation of the astigmatism remained the same, suggesting that the problem may not be the Mangin.
I was planning to do some more testing to isolate the problem and, last night, as a first thing to try, I slackened the retaining ring of the front lens, and Bingo!, the astigmatism was gone. See the second attached test result.
Bratislav reckons that it is as good as astrographs get.
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