If you are interested in more details about M57, you can look for some earlier entries about it. It is one of the objects I quite often return to. If you are visual observer, then you probably have a set of targets you watch, despite the fact you have seen it a few nights ago or yesterday. The same applies for astroimaging. I think I take a longer or shorter shot of M57 every spring.
Last year I imaged M57 with RGB filters and also with hydrogen alpha. Seeing was not perfect then, and stars were bloated. This spring I focused on narrowband data only (both hydrogen and oxygen) and gave up on RGB channels. However the transparency was not as good as I expected, so the nebula outer halo is almost not visible.
I wanted to record nebula internal features called “knots”. Here is explanation what they are according to this paper:
We have studied the closest bright planetary nebulae with the Hubble Space Telescope’s WFPC2 in order to characterize the dense knots already known to exist in NGC 7293. We find knots in all of the objects, arguing that knots are common, simply not always observed because of distance. The knots appear to form early in the life cycle of the nebula, probably being formed by an instability mechanism operating at the nebula’s ionization front. As the front passes through the knots they are exposed to the photoionizing radiation field of the central star, causing them to be modified in their appearance. This would then explain as evolution the difference of appearance like the lacy filaments seen only in extinction in IC 4406 on the one extreme and the highly symmetric “cometary” knots seen in NGC 7293. The intermediate form knots seen in NGC 2392, NGC 6720, and NGC 6853 would then represent intermediate phases of this evolution.
At the narrowband images above some of the features can be recognized.
Image technical data: Date: 19-22 April, 2019 Location: Nieborowice, Poland Telescope: Meade ACF 10" Corrector: AP CCDT67 Camera: QHY163M, gain 100 Mount: SW EQ6 Guiding: SW 80/400 + ASI290MM Exposure: Ha 120x2 minutes, Oiii 90x2 minutes Conditions: seeing average-good, transparency average