Richard, the stretch academy from Adam bBock is a very good tutorial too to understand the concepts and the various approach of stretching (with or without masks, with or without stars, ...). I am sure you will be surprised how you can smooth down your M51 core and raise the spiral arms, and you will enjoy to let speak your data :-). If you capture in alt az with your obsession I think more shorter frames are better than fewer longer exposures. I also have a seestar50 smart telescope too when I travel. Exposures are 10s and the scope refuses to stack above a given altitude as field rotation becomes too strong. It gives incredible result on bright DSOs considering the very small aperture but you have to manage several hundreds if not thousand of subframes.? WBPP of PI does the job for you, you just need a powerfull enough PC or mac to run it ;-). In order to manage the uneven background I had a lot of improvement chasing light leak from the outside in from the UTA and if the gradient is homogenous during your imaging session do not hesitate to take flat frames if you do not already do it. It really change things. I still love visual observations at my dark site but I thought astroimaging would be much more complex than it really is. Especially with all the software existing now to run capture sessions without siting next to your scope
Frederic
Fr¨¦d¨¦ric Ruciak