So far I have only had three attempts at RGB imaging since getting my new scope and camera and on all three nights I have ended up with bad blue halos around bright stars.
The first time I put it down to high level haze coming over. The second time I put it down to bad seeing (had FWHM of 3.8" in 100s images but 2.2" in another part of the sky with 900s Ha). The halos remained after both running a decon on both green and blue which failed so then a convolution on red and green, also failed. The third time I thought that maybe some faint high level cloud may have come before heavier cloud that came over 20 minutes before I finished the blue that night.
Having a 3/3 strike rate with blue halos I started trying to think of something other than poor seeing being the issue. The first thought was that my scope had the colour correction of a fast doublet (unlikely). I then dismissed this as if this was the case my luminance would also be pretty shocking which it hasn't been. This was further backed up as on Tuesday night I had my DSLR on the scope just to make sure, no blue halos.
This then leaves me to either being the filters but never had the problem when they were on my QHY9, they QHY22 does have a considerably better blue response however. Then I considered that maybe it was a UV correction problem and leakage through the blue filter. I have Astrodon Gen II E Series LRGB and the L&B have the same cutoff at shorter wavelengths.
15 minutes ago I got to thinking, at the moment my QHY22 isn't mounted directly onto the CFW (has a ~10mm universal camera adapter thing). Could it be that the blue filter does not converge correctly when it is considerably further back from the CCD, maybe 20mm as a guess?
I may be gettin the same issue with my OIII filter but not to the same extent. Less to do with halos but I have noticed that I continually get a worse FWHM with the OIII than Ha and SII... Or is this normal?
Last night for instance, a very brief check, guessing maybe 3" in Ha and 3.7" in OIII. Haven't run the numbers yet, just did a PSF in my head
I am planning on correctly mounting the QHY22 to the CFW simply for potential flexure issues but could it be causing problems with blue subs?