M101 - My Singular Contribution to Galaxy Season

[The Lazy Astronomer]

In keeping with my usual theme of posting images well behind the curve; as we approach the end of summer nebula season, here's my singular effort from galaxy season: M101 in HaLRGB (capture and processing details to follow in another post below, for anyone interested, and as always, comments and critique welcomed!)

Perceptually, I think it presents best in this orientation (cropped and rotated):

 

Full image (lotta background galaxies in here):

[The Lazy Astronomer]

Details:
Esprit100/294MM/Astronomik filters, data captured throughout Feb, Mar and Apr this year. ~23hrs captured, but chucked the worst ~25% of frames, so total stacks are ~17.5hrs, split as: L=~8hrs, RGB=~2hrs each, and Ha=~3.5hrs. LRGB were all 30s subs @ unity gain, Ha was 180s subs @ 200 gain
Stacking and preprocessing in Siril 
Post processing in PI

Hideously complex gradients in the raw stacks (combination of light pollution and less than optimal flats which unfortunately I wasn't able to reshoot). Fortunately though, there's a lot of background to play with and DBE seems to have saved me.

Tried to process to bring M101 forwards whilst still maintaining something close to a natural star field. As such there was no star reduction done, other than the use of a mask and curves adjustments on the 50 or 60 most prominent stars to try to lessen their impact. It may be my mind playing tricks on me, but I think I can now see some slight dark ringing around some of those stars, so I may need to revisit that and make some slight adjustments.

The general processing steps involved were:

DBE (all channels individually)
Deconvolution (L only)
Denoising with TGV and MMT (possibly went too far with denoising, would appreciate opinions on that)
Stretch L, using a combination of GHS, HT, curves, HDRMT and LHE (with various masks)
Combine RGB, BN and CC, boost saturation and stretch using GHS
Subtract (linear) red continuum from Ha, stretch Ha
Blend Ha into red channel using RBA's PM formula (they might be a little too pink, but I wanted the Ha contribution to be quite subtle, rather than overpowering blobs of red interspersed throughout the galaxy)
A few iterations of LRGBCombine, with saturation boost and slight blur between each one - there was still quite a lot of chrominance noise after this, so I then used quite a heavy application of MMT, followed by a final LRGBCombine 
Many additional curves adjustments to boost faint signal and bring forward more colour (I referenced a Hubble/ESO image to try and prevent myself going too far wrong with the colour - I await @vlaiv's opinion on that!! 🙈😀) 
More slight (masked) curves adjustments to reduce impact of the more prominent stars
Slight application of ACNDR to push down the last of the noise
Final (very) slight colour tweaks
Slight sharpening with MMT
Slight black point adjustment

I should also mention I've been going back and forth on the processing for almost 2 months now - only after capturing all the data did I read about (and then discover for myself) how difficult this one is to process!!


 

[Paul M]

Nice images indeed. 

Although the detail in the crop is exquisite, I love the wide field view with the background galaxies. 

[The Lazy Astronomer]

Here's an annotated version as well

[The Lazy Astronomer]

17 hours ago, Paul M said:

Nice images indeed. 

Although the detail in the crop is exquisite, I love the wide field view with the background galaxies. 

Thanks very much Paul - I'm very much a fan of all the things tucked away in the background of wider-field images too.