Hi Paul,
A fine M20 image you should be proud of especially with only an hour or so of data
Well done indeed !!
To control those big halos around the larger stars ( if your want ) try shorter subs ( 90 sec to 120 sec ) using Gain 100 or Gain 101 ( HCG mode ) on the 533MC , that’s where your read noise drops dramatically but still maintains excellent dynamic range at 13 stops. Just remember you have an extremely fast scope with loads of aperture. Cooling at -10C is again more than adequate to mitigate dark current noise. A great camera !!
Gain 101 on my 2600MC has been tremendous for the past year, a game changer in both South coasts Bortle 3 and Sydney’s Bortle 8
2 to 3 hours of 2min subs on M20 is more than adequate under your beautiful dark Bortle 3 skies as this object is quite bright.
Keep them coming
Cheers
Martin
( currently travelling through Scotland , posted from a tiny town called Laggan )