Rosetta Nebula. December 21, 2019.

Ruslan, the green stars and green hues in the nebula itself don't quite work.

Well, the green in the nebula itself is oxygen. But around the stars—yes, I should try to suppress the halos. I'll try to work on the image a bit more.

There probably isn't that much oxygen there. Look, the stars in the center of your nebula are actually green, which shouldn't be possible in principle.

Alright, Andrey. Honestly, there are a lot of problems—material worthy of the trash bin.
1. Tilted focal plane (sensor or adapter).
2. Strong spherochromatism in the red spectrum from the lens. If the green channel is in focus, the red is blurred. You have to choose or find an intermediate position when focusing.
3. Incorrect back focus distance—the lens is very sensitive to it; the slightest issue and you immediately get seagull-shaped stars in the corners. From the spacers I have, I still can't find the correct distance.

If you're interested, here's a link to the stack and a single frame
https://cloud.mail.ru/public/5fgy/43YKKtWnp

The issues you listed are secondary and require time and new imaging sessions to fix. However, applying the HLVG plugin to this version is a quick task and immediately improves the result. Regarding the rings: in such cases, I use a slightly shorter segment and compensate with thin rings in the threaded connections. Would that approach not help?

It's a complex setup—a Canon EF to M42x1 adapter, then an M42x1 to T2 adapter, followed by a T2 extension tube. The camera itself has a flange distance of 17.5 mm. I just need to order thin spacers (2 mm, 3 mm, and 5 mm) from AliExpress and experiment. Thanks for the tip about the plugin, I'll give it a try.

If you want, I can give you sketches of such rings, I'll print as many as needed on a 3D printer. You only pay for shipping. The rest is a gift.