Last time when I imaged Rosette was 10 years ago. So I recently decided to challenge it again. I imaged it for a full night in November last year, and I found I need more S/N. Last week I further spent two full nights on it, bringing the total integration time to more than 14 hours. The final S/N is nice, but there are some other headaches.
The main issue is the variable seeing. All three nights have different seeing. In one of the nights, the seeing was extremely poor for about 3 hours, and then improved to something barely acceptable. Directly combining all data does not give nice looking stars. So I end up with only using good seeing data for stars, OK seeing data for the brighter parts of the nebulas, and all data for the very dark outer part where noise is higher but details are lacking. Not only seeing is variable, some exposures were probably taken through very thin cirrus. I couldn't identify exactly which exposures were affected. I just know that the stars in the stacked image have very faint, extended halos around them. These halos become visible after a strong stretch. Suppressing them in post processing is not easy. It took me quite some time.
About 40% of the integration were made through the STC Duo Narrowband filter, to suppress the light pollution to get high S/N H-alpha, and also to get more [OIII] and H-beta. This makes the color of the nebulas a little richer.
I prepared two versions, a normal one:
and one with more strongly stretched outer part:
Let me know how you think.
Edited by whwang, 19 January 2021 - 10:14 PM.