The faint red ring that you can hardly see in the centre of this image is supernova remnant CTB1 in Cassiopeia. I have tried imaging this one for years, and this is what I usually end up with. I thought I was being clever this time, so I took 9, 12, 15, 18, 21, 24, 27 and 30-minute subs with the Hyperstar 4 – Yes, that’s a 30-minute sub exposure with the Hyperstar!! And the above is the result – why?
Didn’t think this one through enough. Now I’m pretty sure that with my sky background, I am not getting much signal to noise ratio improvement PER SUB for sub-exposures much beyond 10-minutes. So the above image, signal to noise ratio-wise, is little more than 8 x 10-minute subs. Now you can see, the result is not too surprising. If instead I had taken 48 x 10-minute subs (the usual 8-hours for a good quality image that I have found, experimentally, over 17-years of doing this stuff) then I would have got a 7-fold increase in the signal to noise ratio and almost certainly a far better looking CTB1.
So the quest for a decent CTB1 image continues.