M101, The Pinwheel Galaxy, needs no introduction. It is an enormous galaxy, twice the size of the Milky Way, situated in Ursa Major at around 25 million l.y. away.  (source: APOD).

This was a very long and complicated project, that I started in January 2022... Each year in my light polluted area I have to struggle with the light reflections present in my Newtonian, during galaxy season when shooting LRGB. I have central circle on my images that I could not get rid of, in spite of numerous improvements of my system. Thanks to a kind advice from @Anthony Husson , I changed my coma corrector for a TS Maxfield that is shorter, has 3 elements instead of 4 and makes the system even faster at 3.8. Things got better, but the field still had some gradients, that could be solved this time with DBE.

During my vacations in a fantastic area of preserved dark sky in southern France (Bortle 3), I had decided to take the Newtonian with me. On the passenger's seat, since it's too big to fit in the trunk. He remained silent the whole trip. Initially the forecast was cloudy, but things finally changed. I was able to collect data during 3 nights. The signal was absolutely fantastic, compared to what I have to endure in my backyard. Seeing was exceptional for 2 nights. Finally I decided to drop all the broad band data I had collected during 3 months and keep only the best frames from my voyage. The Ha is from my backyard.

 I performed several tests for Luminance stretching. GHS seems more adapted for nebulae and I was not able to improve the result compared to a classic Masked stretch. I wanted to keep the colour as faithful as possible during processing. I did a Photometric Colour Calibration with a good correlation of the coefficients. All saturation manipulation was global. I was careful not to break the colour balance when introducing the Ha signal.

This is the final image. I am still not decided bewteen the Widefield and the Close-up version. The Widefield has plenty of galaxies especially on the lower right and the star field puts things into perspective, best seen in full resolution. Clear skies !