Quote:
Originally Posted by Bart
That is very, very nice. Well managed and I like the colour so far.
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Thank you! Colours are not to everyone's taste but that's the nature of narrowband imaging
Quote:
Originally Posted by SimmoW
Really deep and crisp there Suavi, and the noise controlled superbly so far. And you haven't been using Darks all this time? So your images will get even better?!
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Thank you Simon. Well, it's not that simple with darks.
So far I have found that unless I have a very large number (more than 120 or so) of dithered subs, applying darks lowers the SNR.
For example, when stacking 120 dithered 15-minute OIII subs, SNR went slightly down for a stack of subs calibrated with darks, while for a stack of 165 dithered 15-minute Ha subs, SNR has very slightly improved when I applied darks in preprocessing.
My guess is that my camera adds only a tiny amount of fixed signal to 15-minute subs and mild dithering is sufficient to control it, and only stacking a lot of subs starts to bring up that signal to measurable levels.
In my recent project with the Helix, even extreme stretching to show faintest signal only 1ADU above the floor did not result in any noticeable glows nor banding in stacks that were calibrated without darks.
Here is an example of a bias-subtracted dark from my camera:
https://www.astrobin.com/363774/?nc=user
Perhaps I could use many more darks than just 38 15-minute ones, but I'm not convinced that this will improve my data in a meaningful way.