This is the Wizard Nebula. I’m told it is supposed to look like a wizard in a pointed hat and gown with open arms. I imaged this over two nights under very bad weather conditions and a bright moon.
I attempted and abandoned some S2 – the signal was weak and too many subs were trashed. At the end of the two days I applied more than my usual rigor to the frame selection process and ended up with just 100mins each of Ha and O3.
Stacking just the best subs didn’t change the star sizes but the fainter ones were sharper, over-all contrast, range and noise was improved (so spending the time up-front to select good frames is really worth it). O3 was still weak but I decided not to push it too hard. I applied the halo reduction technique for the O3 described here it works surprisingly well.
I’ve combined the signals as R=Ha, G= 0.3*Ha +0.7*O3, B= O3. The central blue area of the nebula was enhanced using an O3 range mask and just increasing the blue saturation a little. This was quite tricky to process and easy to overdo.
After imaging this nebula, I’ve purchased a replacement O3 filter. For future narrow-band projects I’ll be swapping out the notorious-for-halos ZWO 7nm O3 filter for the Baader 6.5nm (new for 2021) O3 filter that is supposed to have much improved antireflection and halo reduction coatings. I plan to do a side-by-side comparison in a mini-review just to see if the Baader filter is worth it in my setup.