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 Post subject: The M81 Group
PostPosted: Mon Mar 26, 2012 8:08 pm 
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Hi folks,

I pulled an all-nighter last night with serious imaging starting at around 11 pm and finishing with the dawn. Here is the result:

      M81, M82 and NGC 3077
    Image
    Click the image for a larger version.
I had intended to continue imaging this evening but a preliminary play with the data (8 x 1000 second subs of each of red, blue and Hα) convinced me that it would take a lot more telescope time to significantly improve on the final image so, being pretty cream crackered, I think I'll take the night off instead! I've added processing notes at the end of this post on the assumption that they will be of limited interest to most.

To gain more from the image you might enjoy the article View Of New Hydrogen Clouds In The M81 Group Of Galaxies over at Science Daily. M81, M82 and NGC 3077 are all physically connected by hydrogen gas. M81 (the large spiral galaxy) had a pretty severe effect on M82 (nearer the top) due to a gravitational close encounter in the past but it's not obvious from the image above that NGC 3077 is part of the same complex.

Bob.

Processing

TEC 140 telescope, ML16803 camera, Astrodon Red, Blue and 3 nm Hα filters. Eight 1,000 second subs through each filter.
Processing in PixInsight and Photoshop.

After the usual calibration and alignment I combined the red and blue images to get a synthetic luminance on the assumption that there wasn't anything specifically green in the field of view. That luminance image was then used as a synthetic green and combined with the red and blue images to get an RGB image. It was also processed separately in its "luminance" role and for the first time I used PixInsight's StarMask abilities to run an HDRMultiscaleTransform with the stars protected. That allowed me to bring out more detail in the galaxies. I then used the R(G)B data to colour the processed luminance and did a histogram stretch and exported to Photoshop. The Hα data was also combined, stretched and exported to PhotoShop. Once in Photoshop images were tidied up and the Hα was given a spot of red colour before being combined with the main image. Then, being a glutton for punishment, I did my usual star extraction to end up with "Just Stars" and "No Stars" images. Both were passed back through PixInsight where a spot of deconvolution was applied. Settings for that operation were quite aggressive for the "Just Stars" version and minimal for the "No Stars" version. Back into PhotoShop where they were combined again and a spot more tarting up took place.

Deconvolution of the stars seems very good at washing out most of the colour but on the other hand I'm not a fan of violets or deep reds in star images as, with a few notable exceptions, stars are rarely that coloured. I did try hard to retain and enhance the galaxy disks. The blue colour seems a little too prevalent to be down to star burst activity so I'll hold up my hand and plead guilty to a heavy hand with the saturation. The more intense reds are down to Hα emission and while the colour is about right the intensity is way up compared to regular black body emission but without that boost the Hα emission nebulae in M81 and M82 wouldn't show.

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 Post subject: Re: The M81 Group
PostPosted: Mon Mar 26, 2012 9:13 pm 
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If you can see Holmberg IX that clearly then you should be able to see traces of the IFN too - but not with the black point pushed that hard. I think you have enough data to pull out a ton more stuff - but now you're entering the second (and equally difficult) part of deep-sky imaging - the dreaded processing :D
Greg

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 Post subject: Re: The M81 Group
PostPosted: Mon Mar 26, 2012 9:48 pm 
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Hi Greg,

I'll have a close look tomorrow when the main 'pooter is back on but nothing jumped out at me when I was adjusting the PixInsight Screen Transfer Function while looking at the unstretched stacked data. Maybe it was there but I didn't recognise it or maybe it really is lost in the noise and I need to go deeper given I'm shooting at f/7. Thanks for the heads up that there is more going on in the region than you see in the usual web images or astro-photography guides.

I'm also going to have to see if I can cut my round 72mm IDAS LPS filter down to 50mm square as it's no longer needed for DSLR duties and I think it will be helpful when looking for the really faint stuff to be able to expose for luminance directly without the pestilential local sodium street lights swamping the signal. And then there's binning. So much to learn... :twisted:

Update: For those like myself who scratched their heads at Greg's mention of IFN check out the article Integrated Flux Nebulae.

Bob.

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OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: The M81 Group
PostPosted: Tue Mar 27, 2012 7:43 am 
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Apologies for not spelling out the IFN bit, I forget (with the good astro work that goes on here) that it isn't an astronomy forum :D The IFN won't "jump out at you" on the contrary - you are more likely to interpret it as a gradient and try to get rid of it with gradient Xterminator or somesuch. Lots of people have spent a great deal of time trying to get rid of the M81 gradient (with limited success of course).
Greg

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 Post subject: Re: The M81 Group
PostPosted: Tue Mar 27, 2012 5:23 pm 
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Hi Greg,

Oh, you mean this: :P

    Image
I had to do an extreme stretch in PI even to see it and, of course, that totally blew everything else in the frame. In the end I exported that extreme stretch into Photoshop and isolated the IFN by hand as my normal star removal routine has a very nasty effect on image noise of which there was plenty, most of it the IFN. :roll:

There's actually quite a bit more IFN to see than shown above but I chose to tone it down considerably as there were too many artefacts around the galaxies and bright stars because of the way they were originally processed. My choice of IFN colour was also pretty arbitrary but now that I know to watch out for this stuff I can hopefully re-jig my processing as needed for a more integrated image.

Bob.

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OM-D E-M1 + ED 12-40mm f/2.8, H-F007014E, M.ZUIKO DIGITAL 45mm 1:1.8, M.ZUIKO DIGITAL ED 75mm 1:1.8, L-RS014150E.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: The M81 Group
PostPosted: Tue Mar 27, 2012 5:48 pm 
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Ever wished you can move into the middle of nowhere (no light pollution) and see what you could pull out then? Until that happens, I think you're doing a fine job of extracting what you can!

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 Post subject: Re: The M81 Group
PostPosted: Tue Mar 27, 2012 5:59 pm 
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Hi popo,

Thanks for the kind words. One thing I have discovered is that some of the light pollution I used to suffer with a DSLR was actually thermal noise! How much I won't know until I can image through an IDAS filter but with a bright sodium street light less than 20 metres away I'm not holding my breath for a hugely good result.

Bob.

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OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: The M81 Group
PostPosted: Wed Mar 28, 2012 10:38 am 
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I have six (yes that is actually 6) sodium street lights within 50 metres - using a DSLR the garden is lit up like a Christmas ornament. Still manage to do the work you see with an IDAS filter. Won't be able to in 2 years time when they will replace the sodium lights with broadband LED lights. Currently looking to house move :cry:
Greg

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 Post subject: Re: The M81 Group
PostPosted: Wed Mar 28, 2012 11:49 am 
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At the risk of going way off topic, just this morning I was wondering if it would be economic to start an "astronomers B&B" in the middle of nowhere?

Back to more urban life, this country seems to be lagging others in the use of directed light output from streetlights. I wonder how much benefit there would be if they put more of the light in a downwards direction than everywhere at once.

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 Post subject: Re: The M81 Group
PostPosted: Wed Mar 28, 2012 2:52 pm 
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Great image with lots of data to pull out.

Nice flux showing and a great discussion.

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 Post subject: M81, M82 and the IFN
PostPosted: Tue Apr 10, 2012 2:00 pm 
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Hi folks,

I thought it was about time I reprocessed my data with a view to taking up Greg's (cybermystic's) challenge to show the IFN (read all about it here) which he rightly believed I should be able to see. Here's the result:

    Image

    M81, M82 and the IFN (Integrated Flux Nebula)

Quite a processing challenge starting from 8 x 1000 second subs of each of Red, Blue and H-alpha taken with an ML16803 camera through a TEC 140 'scope. The red and blue data was used to create a luminance channel which also subbed for Green to produce an RGB image which was subsequently used to colour the final luminance image. The luminance image destined, as all were, for processing in Photoshop was produced by combining, using an HDR technique, a normal stretch of the luminance data and an extreme stretch designed to really bring out the IFN. I also took the opportunity to apply some "multiscale" processing to the image to enhance the detail near the core of M81, all courtesy of PixInsight. With the IFN boosted in this way the challenge, as I see it, is to manage the transition between what is part of the galaxies, which are a very long way away, and the IFN which is local to our own galaxy.

I took a copy of the luminance image and manually removed all the stars, a process which is extremely tedious but necessary IMHO as my usual "Dust & Scratches" star removal routine really churns up the low level noise in the image and, unfortunately, it is exactly that low level noise which is host to the IFN signal. That allowed me to process the IFN quite separately in order to try and enhance the detail while controlling the noise. The galaxies were still there, of course, but I found it was possible to apply a Photoshop curve which effectively took them out in a loving and gentle way when the IFN was added back to the other components. The shape of the curve had to be tweaked so that adding in the "IFN" image (using a Photoshop Screen layer) was possible without having to airbrush out the galaxies themselves. There is still a slight artefact evident as a bluish extension to the disc of M81 but short of manually desaturating it my only other course of action would be not to colour the IFN at all.

The original luminance was also used to produce a "No Stars" and "Just Stars" image. The "Just Stars" image was fed back into PixInsight for a spot of deconvolution while the "No Stars" image, basically just the galaxies, was given a final spot of contrast enhancement. The two were combined to produce the final luminance image for the stars and galaxies. That was coloured by the RGB image produced earlier as the next Photoshop layer. The processed IFN image was added to the layer stack and coloured via a clipping adjustment layer. The choice of colour was arbitrary, although informed by some other images out there on the Net, and maybe for some colour shouldn't be applied at all. Finally some H-alpha extracted for just the galaxies was added. 1 used several clipping adjustment layers to tweak the various components and try and achieve a reasonable balance.

I imagine there must be a simpler way of doing all this. Combining H-alpha and RGB can be tricky enough, my being a bit of a newbie, but the IFN is fainter still compared to much of what is visible and if there are any recipe books for exactly how all the ingredients should be combined I haven't found it yet. The image is the result of a couple of days of processing so I hope it was worth while. :)

Bob.

P.S. The light background of the forum doesn't do the IFN any favours. I've also posted over at the Stargazer's Lounge where there is a darker background.

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OM-D E-M1 + ED 12-40mm f/2.8, H-F007014E, M.ZUIKO DIGITAL 45mm 1:1.8, M.ZUIKO DIGITAL ED 75mm 1:1.8, L-RS014150E.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: The M81 Group
PostPosted: Sun Nov 04, 2012 12:31 pm 
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Hi folks,

Rainy couple of days so I reprocessed:

    Image

Bob.

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OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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