this is my first post here. Be gentle
Like many other photographers I’ve been busy trying to take pictures of the great comet Neowise. Taking the pictures was fun, but the post processing has been quite frustrating. First and foremost I assume it is ME who messes things up. But with me there are many other photographers having the same issue with Neowise, especially in SiriL processed images, so maybe it’s a general misunderstanding on how to process these images properly in SiriL. So if you experts could give me a few pointers on what I do wrong, or what I should improve, that would be GREATLY appreciated. Here we go.
I am fairly new to SiriL. I have read the guides and watched many videos, but this specific issue I have not encountered.
The problem is there is an ring artifact with a very dark center which becomes visible after BG subtraction… No it doesn’t matter which lens I use or at which focal length (I have not tried stacking <70mm) or on which day I take the images (low/high moisture), if I use 10 subs, or 100… it always appears. When I try similar or deeper stacks on star fields, I do not get it… so if it is a flat field problem, then why I don’t get it for the star fields?
I pre-process the images with Bias and Darks. (No flats, which ‘could’ be the issue), register, stack, remove green, color calib and then I attempt BG subtraction.
Usually take 15 samples per line avoid any samples near the comet’s tails, try 4 harmonics, 3, 2, 1, or a combination to get it as flat as I can. In the manual there is a UI where you can see the BG model, but I assume that is not available for MAC as I can’t seem to locate that. I tried taking samples in the high BG regions only, high BG regions only, only along the sides of the comet, leaving all the middle lines sample free… none of which works…
Here is an example. (Yes I also don’t understand how the stretching correlates to output, but that’s a different topic). ANY help is appreciated… you experts probably recognize the issue from a lightyear away.