[2020BC (Bill Christie)]

Asimov, hee hee. After all my waffle and checking through the image below in the original posting the core isn't actually masked. At the moment I have several different versions of this that I've processed in slightly different ways and posted on different sites. If we look again the image we refer to in the original post has a small burnt out region that hasn't been processed out. Looking through the original RAW stack the burnt core is exactly the same size as the posted processed version. Looks like it's just the way the camera rendered it with 3 mins in the ED80. The ED80 is f/7.5 and I did use the UHC-S filter - could this be the clue/info that you need? An 8" at f/4 @3mins will have more of the core burnt, even more so if it's unfiltered.

Attached here is an actual masked version with the core replaced with a 30 second exposure from the 80ED (UHC-S) (one that I nearly threw away because it was a focus test).