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Hi Ray,
Thanks for your reply.
I don't think there is anything stray about the light. All the fittings are quite tight screw together, and the pattern is quite symmetrical.
I had a reply from Terry at SX. He suggests it "must" be the extension barrel threads (which run the entire length of tube from barlow to FW) and said to try putting black matt paper over the threads. Of course I don't have any on hand. He also suggested making a cardboard aperture stop just before the FW. I'll try the first idea first. The second seems quite fiddly.
BTW, are you using 1.25" filters in the SX wheel? Do you see vignetting? Your system is pretty fast so I wonder if that is more of an issue for you?
I seem to attract hard problems like a magnet. I think equipment hates me.
The tests last night at 2x2 were just for speed and small file sizes. I fully intend to use the full resolution of the barlow, otherwise, as you correctly point out why bother with the barlow at all!
Peter
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