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M101 - Pinwheel Galaxy (Esprit 150, 6hrs)

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There have been lots of really excellent M101's posted on SGL of late but for the record here is my attempt.  This is the final data set of my spring galaxy imaging (although actually I captured the data for this before any of the others on a couple of clear nights in late March and I will be posting a reprocess of the Whale Galaxy at some point).  This was first light for my new Esprit 150 and sadly I didn't nail the guiding (the scope is at the limit of what my CEM60-EC can handle) which has impacted on the blue channel in particular.

I took 60, 180s subs in each channel and stacked the best 40 of each for a total integration time of 6hrs.  3 minute subs are just enough, I think.  Only the very centre of HIP68503 (TYC3852-468-1) and a couple of the other bright stars were saturated and the signal in the galaxy was OK but I think 300 second subs would have produced a better result on the outer spiral arms so I think that I will use 5 minute subs for this sort of target with this set-up in the future.

Kit was CEM60-EC; SW Esprit 150; Atik EFW2 with Astrodon filters; Atik OAG with a mono QHY5L II; Atik 460ex.  Data acquired using SGPro, guided with PHD2 and processed in PI and PS.

This version is the straight RGB, processed as best as I can:


This is a version with all 120 of the R,G, and B subs stacked together to create a synthetic luminance.  Whilst I didn't go crazy sharpening the resulting luminance layer, I think it does add a bit of detail and contrast.  As an aside, in the second StarGaZine instalment, Nik Szymanek (for whom I have the greatest respect) was not convinced that a synthetic luminance adds anything, if I understood correctly because you obviously don't actually have any more data.  However you are, of course, utilising that data in a different way.  Stacking all of the subs using an algorithm like sigma clipping gives a different result to layering the 3 individual stacks (not least because you have 3 times the number of subs for the low-signal sky background which I'd argue is more or less the same through each filter unless you have bad light pollution).


All that said, as I have been discussing with @MartinB, I think in future I will return to putting most of my effort in to getting a good luminance data set and bin the colour as I have done with previous images of M51 and M81.

Finally here's the annotated version from PI.


Apols for the long post!

Clear skies, Ian

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Super image, I also think the second image is a little sharper than the first.  mmm.....I wonder can APP produce a synthetic luminance layer?  I'll look into that as I haven't yet downloaded the PI trial.

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Very many thanks for all the likes and comments, I really appreciate it.

3 hours ago, tomato said:

Very nice, stunning detail and a great FOV with the Esprit 150/Atik 460 combination. I also like the silvery blues of the spiral arms.👍 

Thanks @tomato.  I neglected to mention that I had to crop this more than I would have liked as I made a complete pigs ear of the framing.  I made my own adapter to couple up the field flattener to my Atik OAG and removed the imaging gear to check some measurements... When I put it back I set the orientation of the camera by eye and didn't check a reference image - rookie error!

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2 hours ago, rubecula said:

Super image, I also think the second image is a little sharper than the first.  mmm.....I wonder can APP produce a synthetic luminance layer?  I'll look into that as I haven't yet downloaded the PI trial.

Thanks Robin.  I've never used APP but it's literally just a case of bunging all of the registered subs together and stacking them so unless APP reads the fits header, sees the filters are different and refuses to stack them (which would be a bit odd) I'd have thought you'd be OK... and even then you could edit the fits header if you really had to.

It's nice to see a consensus that the synthetic luminance has improved the image but as mentioned earlier I think capturing genuine luminance data is the way to go really.  That's my plan for the future anyway... 

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I don't have enough knowledge to comment in any sensible way on your processing.
All I can comment on is what I am looking at, and that is simply a stunning Image of  what I believe to be difficult Galaxy 
 for Astro. Photographers t o Image  It is  a lovely sight, and as for your long post,  make them  pages long  if they include Images as good as this.
Ron. 👍

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5 hours ago, MartinB said:

Another beautiful galaxy image Ian.

Thank you so much Martin - that's very kind.

5 hours ago, Kluson said:

Wow what a beautiful picture

Thanks for taking the trouble to comment Kluson - really appreciate it.

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Really great M101 Ian! If i didn't already know it i would have guessed this was 2 or 3 times the integration. 

For me the synthetic Lum version has added a lot. The sharpening looks spot on. 👍

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Thanks Steve, thanks Ciaran...

I'm really delighted with, and appreciative of, all of the positive comments - thank you so much!  Having been away from the hobby for a bit I've had to re-learn an awful lot and, as a new user of PixInsight, learn that for the first time.  I'm feeling that my processing is just about getting back to where it was before work got in the way so these comments are really helpful in confirming that I'm heading in the right direction.

Thanks again!


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