Quote:
Originally Posted by Paul Haese
Now this I think is important and might pertain to your scope. Check the actual secondary fixing to the stalk. Mine was glued down with a very wide narrow smear of silastic. That caused astigmatism and I think I can see some in your image. The way to test this is to take an image intra and one extra from focus. If star shapes near focus on both side have an oval on both sides and each oval is 90 degrees to each other then you have some astigmatism. It's worth a check to eliminate this issue. I reglued mine down with 3 small blobs of aquarium grade silicone and supported the stalk with match sticks to keep them up high enough so as not to smear. This eliminated astigmatism.
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I got caught out by that one when I glued back my secondary after having it recoated. It is incredible the pull silicon can have on even the thickest piece of glass when it cures, even three small dabs. On my C11, too much of this stuff managed to stress the glass between the baffle tube and the bore in the primary and we're talking of about 100mm of thickness at that point in the mirror because it is bell shaped. I had to slice parts of it to release the pull.