[JA]

Hi M,

You already had some good input on the possible cause of your noise and vignetting, but here is another perspective. You mention that you use ...

Originally Posted by DaBris

... a Skywatcher 72ED, a .85x reducer and the Canon is connected via t-ring.

Now I can't find the official Skywatcher imaging circle specification for the Skywatcher 72ED, from an official source, see...https://skywatcheraustralia.com.au/p.../evostar-72ed/


but, I'm willing to venture that given its size, it won't support a full frame imaging circle without vignetting and more likely has something around a 33mm image circle like the larger Skywatcher Espirit 80ED, and similar spoces, per specs here...https://www.bintel.com.au/product/sk...v=322b26af01d5

If we take it that it has a 33mm image circle, then a .85x reducer, will reduce that to an imaging circle of ~28mm, which is close enough to the diagonal of the Canon 60D sensor (26.8mm, based on Horiz22.3mm & Vert14.9mm) to have vignetting starting to show, especially as the degree of stretch on the image is increased.

Also as already mentioned the filter may be an issue. Try with and without under the same conditions to rule it out. Sometimes the pass band of filters can change slightly with reducing focal ratio and although that usually occurs at much faster f/ratios, who knows? Maybe the effect can been seen earlier in your application due to a combination of factors.

Best
JA