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Old 17-05-2019, 05:19 PM
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Paul Haese
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Join Date: Jan 2009
Location: Adelaide
Posts: 9,496
AG12 correction resolved

It has taken nearly 12 months to go through every conceivable permutation of what could be causing the poor star shapes on the frames of the AG12.

First I obsessed about the collimation for months, many hours of checking and rechecking. Ensuring I was improving my accuracy all the time.

Then I went over all the adapters on the scope. I checked the ones that OOUK had made and the ones I had made by Precise Parts. A friend made an adapter and adjusted the OOUK ones to ensure everything was 100% square. The OOUK ones were not square and threads were running out by several thousandth of an inch.

Then I went over the installation and gluing of the mirrors in their respective cells. Making sure nothing was pinching or causing astigmatism. I found some astigmatism in the secondary but fixing that did not fix the problem.

Then I checked over the position of the focuser and the centre of secondary. That checked out fine.

In the end I took the advice of a friend who suggested that it was the corrector. I ran a laser through the corrector on a flat mirror and it was a little out. However when I ran the laser through the corrector and the scope at the same time it was significantly out. Even though the scope showed perfect collimation each time. So I ran another experiment which demonstrated that the threads on the Wynne corrector were too loose and not square to the line. I got a different result each time rotating the corrector around and using the tightening ring. After that I decided to use another corrector. I had to wait for some parts from TS in Germany which took some time but it confirmed what I was thinking. The OOUK Corrector is faulty.

The attached image confirms that theory. Taken with a TS GPU corrector. To boot it is sharper than the AG12 corrector. This image shows the corners and the centre. All looking good.

Now to get the corrector replaced or refunded for the cost of it.
Attached Thumbnails
Click for full-size image (Test image GPU to AG12.jpg)
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