Good first effort! I think the focus looks a little soft and there may be some over-sampling and guiding issues.
- Do you have a Bahtinov mask? For a manual focuser this will be a big help.
- Make sure to check collimation from time to time and adjust if needed but unless your scope gets banged around a lot it not really something you need to do frequently. On my SCT I always do a quick check before I start an imaging run.
- What camera did you use for guiding and how were your guiding numbers? With your setup the resolution per pixel is around 0.63". That means you need to be guiding below that which is not at all easy even on an well tuned and aligned EQ6. Try using 2x2 binning instead which will give you 1.26"/pixel and is much more forgiving in terms of guiding.
- Your focal length (with reducer) is around 945mm which is reasonably easy to work with but close to the limit where guide scopes get in your way and OAG's offer a better alternative.
- What did you use for polar alignment? The polar scope or an app? It's good to learn how to polar align with the polar scope. However, like driving a manual transmission, once you learn it you don't need it anymore (unless you enjoy it). My advice is to polar align with your camera and plate solve with NINA, Sharpcap or the ASIAir for example. Plate solving is much more accurate than manual alignment (my experience but others might disagree).
- Your camera is a great camera but is more appropriate for Solar System lucky image videos (planets, Moon, Sun etc) or doing EAA with live stacking. If you get into DSO seriously then you'll want to get a cooled camera with a larger sensor (budget permitting).
- For emission nebula you will greatly benefit from any of the various dual narrow-band filters. I really like the l-Ultimate. For broadband targets like galaxies and globulars then the only filter you can really use with a color camera is an IR/UV filter which will cut down on star bloat (since your camera is sensitive to those wavelengths and thus they won't be in focus) The various light pollution filters really don't work in my opinion since most light sources these days are broadband LED and are not possible to filter out (as opposed to low pressure sodium or mercury vapor)
- Take shorter subs (like 30-60s) in a light polluted environment.
- You can cut down on light pollution gradients in post processing. I'm not familiar with Siril but this is easy to do with AstroPixelProcessor or PixInsight.
1. Yes i have it, but my mistake was to no check the focus time to time within the 4 hours
2. Collimation is quite accurate, I collimate in focus using metaguide.
3. The camera is an ASI120MC on a 60/240 (f4) SVBony guidescope, guiding nubers was not so great variing within 0.55 and 0.85 rms, dont know if because of ugly seeing, (then sonsider I have the EQ6-R from less than a moth, I was used to use an alt-az mount with wedge)
I will try your suggestion 2x2 binning or to add a barlow a 2x to the guidescope
4. yes, I'm considering an OAG, but will see in coming months, but I'm considering also to buy a scope more suited for DSO
5. Polar alignement done with TPPA plugin of Nina, but need to improve something as I never get consistent values, I means if I repeat the process azimut is quite stable (±10 arcsecs within the two attempts), altitude instead is always quite off (some times by ±1 / 2 arcminutes).
6. Yes, a cooled camera in in the list... need to define the bujet ( ), in the meatime I will try to improve my-self with the DSLR for larger targets
7. 1st thing to do is to move to countryside location, to avoid at least very near light sources
8. Yes try to use short exposures will be my next attmpts