NGC6888 Crescent Nebula

 Posted: Aug 29th, 2026
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NGC
IC
HD
Technical Info
Telescope/Lens: celestron 80ED f 7.5/600mm
Camera: ZWO ASI 533MC Pro
Mount: Sky-Watcher Star Adventurer GTi
Guide Scope: svbony sv165
Guide Camera: zwo asi662mc
Software: Siril, pixinsight,PS
Accessories: reducer sv193 ×0.8 asiair mini
Exposure:
80 x 180" ISO/Gain: 100 - LAIDA dual band Ha OIII 7нм
Green, Bortle 4 zone:
 Kichmengskiy Gorodok Vologodskaya Oblast, Россия
 Aug 28th, 2026
4 h 0 m
141
Resolution: 2950x2942 px
Scale: 1980 KB
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Comments

How do you align the background in the Ha channel with so many background clouds?
30 Aug, 2026 Reply
Nickolay Replied to Timochkins
I do automatic background removal in PixInsight and don't overthink it, but you can also do it manually by placing targets (little squares) there, just like in other programs.
30 Aug, 2026 Reply
Timochkins Replied to Nickolay
I actually stopped feeling the need to align the background altogether once I got rid of light leaks with the ToupTek filter wheel.
30 Aug, 2026 Reply
Nickolay Replied to Timochkins
When I started processing channel by channel, I also sometimes forgot to flatten the background, since there's not much difference anyway.
30 Aug, 2026 Reply
Timochkins Replied to Nickolay
Previously, light pollution mainly came through the viewfinder of a DSLR and through the manual wheel from Svbony.
30 Aug, 2026 Reply
Nickolay Replied to Timochkins
Well, with equipment like yours, you can simply stack the channels and get a good result)
30 Aug, 2026 Reply
Timochkins Replied to Nickolay
It only seems that way :) Until you realize that you need to refocus for each filter and when the temperature changes by a couple of degrees, and so on and so forth.
30 Aug, 2026 Reply
Nickolay Replied to Timochkins
Yes, that's true. There, the focus correction is supposedly calibrated for each filter, but I only know this in theory.
30 Aug, 2026 Reply
Timochkins Replied to Nickolay
I focus manually, since I'm using a Bahtinov mask anyway.
I also take separate flats for each filter. Moreover, it seems the filter wheel needs to be assembled in a clean-room-like environment. Since it doesn't seat perfectly precisely, the dust on the filter must always stay in the same place for the flat to work correctly.
30 Aug, 2026 Reply
Nickolay Replied to Timochkins
Then patience to you, it definitely won't be superfluous—mono and everything by hand is quite the hardcore.
30 Aug, 2026 Reply

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