This is my second "bigger" project (after M51) and I really love it. We recently had an unexpected amount of clear skies in Germany and I used four of the moonless nights to capture this beauty. I blasted 22 hours of photons on my sensor, in order to learn something about the necessary total exposure time (I'll stack the same object with 2h, 6h, 12h, and 18h later this week - there I want to investigate the impact on the grade of detail). See Revision C.

I not only captured M101 because it's a good fit for my 1000mm setup, but also because I really enjoy capturing galaxies. And this is a big one ;)
M101 is 170.000 light-years across (Milky Way = 120.000 ly) and 20 million ly distant. It contains about a trillion stars (Milky Way = 200 billion)  and was added to the Messier Catalogue as one of the final entries.
M101 has a high population of HII regions, which I colored with a slightly more aggressive red-tone to produce a better contrast over the bright spiral arms full of young blue stars.
The tidal forces of dwarf galaxy NGC 5477 (and 4 other companions) are responsible for M101's asymmetric shape.

Revision G Starless Version - it's always fascinating to see how nondescript so many galaxies hang around in our pictures.

Revision C shows a stack of the same data (equally split among the three sessions) with 2h, 6h, 12h and 18h of exposure time. All images have been stacked and cropped with the same settings.

Revision F shows a complete reprocessing of the 20h RGB and 2.5h Ha stack. Smaller changes are the usage of NoiseXTerminator and StarXTerminator and a slightly different color calibration. But the main difference is the improved details in the cor as well as a better Halpha integration. I uses a continuum subtraction, in order to better distinguish the hydrogen-knobs from other luminosity and noise.

I also used a linear sharpening (on 32bit data in APP) before stretching and sharped again after stretching (on 16bit in PS). I did not apply the sharpening on the stars or background. Additionally i used some selective sharpening on the spiral arms.

I used this data to even further investigate on getting out more details: https://www.astrobin.com/2cpq82/