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PostPosted: Sun Jul 29, 2012 11:15 am 
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Hi folks,

We had an unprecedented sequence of clear nights here in the south of England last week during which I was able to have a first attempt at our nearest large galactic neighbour M31, more commonly known as the Andromeda Galaxy (Wikipedia). This is also my first attempt at processing the data and, as usual, there are so many choices to make along the way that I'll flag this up as a preview so that I can revisit it later and reprocess as needed. I might even link to the full size 4096 x 4096 pixel image at that point but for starters here's a 1024 x 1024 pixel version:

    Image

    'Scope: TEC 140
    Mount: ASA DDM60 Pro mount - an awesome bit of kit as even the 1,500 second subs were unguided!
    Camera: FLI ML16803
    Subs: 5 x 1,000 seconds using each of Astrodon Tru-Balance RGB filters plus 10 x 1,500 seconds using an Astrodon 3nm Hα filter
    Software: PixInsight and Photoshop CS6

The colour of the stars and the majority of the galaxy is muted. I could have pushed harder, and I might yet do so, but aesthetically I prefer to avoid a heavy hand. The Hα emission nebula have to be boosted to be visible and, of course, the brightness and contrast of the galaxy has to be adjusted to show up structure.

The Hα processing went a little differently than I've been used too. Combining the 10 x 1,500 second subs produced an image with a fairly high contribution from the stars as well as from the emission nebulosity. Lacking a narrowband continuum filter I used PixInsight's PixelMath to subtract a portion (1/15th) of the Green signal from the Hα one using linear (unstretched) data. Green because my assumption is that that colour is pretty isolated from Hα and Hβ emission, the proportion being chosen by trial and error to remove as much as possible of the Hα signal while not clipping any areas "below" black. That left me with a very much reduced core which was actually pretty distinctly separated from the spiral distribution of the emission nebulae. I still had to remove quite a number of stars, carefully avoiding removing small patches of nebulosity by doing a blink comparison with a "Stars Only" image derived from the RGB data but once that was done and the result tidied up and coloured I added the result to the RGB image.

Comments and criticism welcome.

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
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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PostPosted: Sun Jul 29, 2012 1:14 pm 
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I've never seen it like that before! That's good, by the way. The milky appearance looks a bit odd as I guess I'm used to seeing the more intense visible light representations typically with a warmer core and cooler outer regions, punctuated by the dust lanes. Taking the image as is, I think I like it with a bit more pop, just a touch of unsharp and increased saturation to bring out the core colour and dust lanes more.

The diagonal tilt is starting to do my neck in as I keep finding I also tilt to view it... was that intended to get it to fit better?

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PostPosted: Sun Jul 29, 2012 1:29 pm 
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Hi popo,

Glad you like it even if it does do your neck in. :lol:

The tilt is the default given my camera is normally aligned north/south/east/west. If M31 had a different alignment I'd have had to rotate the camera to get the galaxy to fit even as well as it did. Ideally I'd need either a bigger sensor :twisted: or a focal length reducer to be sure of getting every last photon in as the only cropping I did was 48 pixels along each side.

Bob.

P.S. The image is also getting some nice feedback over at Stargazer's but it's early days and I'm sure it will attract some other feedback in time.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
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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PostPosted: Sun Jul 29, 2012 1:37 pm 
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Rotated or not, you know you want to mosaic it ;) At least to get the upper left end...

Ever thought about other narrowband filters? Even if I have no idea if it'll be any real use on an object like this. Still, give it another month or two and this might start appearing early enough for me to give it a go myself.

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
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PostPosted: Sun Jul 29, 2012 2:04 pm 
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Other filters are certainly on my wish list. Not sure that I'd see much benefit on M31 but I haven't done any research on that.

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
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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PostPosted: Mon Jul 30, 2012 9:25 am 
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Hi folks,

As this isn't a specialist astronomy forum it might be useful to put the image above in context. The Andromeda Galaxy is in many ways similar to our own Milky Way although it's a bit larger. If we were to transpose the position of our own Sun into Andromeda then think somewhere like the outer ring of reddish nebulosity. That explains why at some times of the year the Milky Way is much less impressive than at others.

Many of us, certainly those who spend time away from the light pollution typically generated by large towns and cities, will be familiar with the constellation of Orion and, in particular, the faint misty patch that forms part of Orion's sword - check out the forum thread Your best shots of M42 - the Orion Nebula!. That is a region of gas and dust which plays host to star birth and the heavier newly born stars emit copious amount of energetic photons. That can give them a blue tinge but it also has the effect of lighting up the gas and dust cloud which gave them birth and one of the strongest components of that light is due to hydrogen, the most abundant element in the universe, which, in the visible spectrum, emits both a deep red and a less intense bluish component. That red emission is specifically selected by a Hα (hydrogen-alpha) filter so if you look at the spirals and clumps of red in the image above and think that each of those is a site of star birth then you won't be far wrong. I think I am also right in suggesting that something the size of our own Orion nebula, which is fairly close to the Sun in galactic terms, would be pretty small in the image above.

It's very easy to look at a spiral galaxy and make the analogy with a Catherine wheel. That's not what is going on but maybe a discussion of compression waves is beyond where I ought to go here. Suffice to say that the structure is part of a dynamic process which includes star birth so the actual composition of the disk isn't as chemically differentiated circumferentially as one might be tempted to believe. That's not so true when one travels out from the center towards the edges however. To see why it's helpful to remember that stars are factories which release energy by fusing light elements such as hydrogen into heavier ones. The really heavy elements (heavier than iron) actually reverse that energy flow as they are synthesised so they only get made in any quantity in violent explosions (supernovae) but the lighter elements can also be returned to interstellar space in a less spectacular fashion (think "solar wind"). The net result is that as star formation continues over the lifetime of a galaxy larger and larger proportions of "star dust" (elements heavier than hydrogen) get incorporated into the new stars and, of course, the planets that orbit them. Without that star dust we wouldn't be here!

There are even clues to this in the image above. The stars of the central bulge tend to be older and cooler and the region is not so conducive to fresh star formation. Star formation is much more easily triggered in the outlying disk of the galaxy by those compression waves I referred to and those spirals of Hα emission are the smoking gun. They travel around and through the disk and as each new generation of stars is formed, the heavier stars living short but intense lives which end as supernovae, the material of the disk is enriched with the heavier elements such as those which make up you, me and the planet we live on. No surprise then that we live on the outskirts of our own galaxy. 8)

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
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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PostPosted: Wed Aug 01, 2012 9:54 am 
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Hi folks,

The earlier image was a "first attempt" not only at capturing M31 but also at processing the data. With the benefit of both feedback and a little more thought I've tweaked the processing so here's the result:

    Image

If you click the image you can view a 2048 x 2048 pixel version. For the new version I've restored the fainter outer parts of the disk (should never have got excluded - finger trouble with a curve, I'm afraid) and removed the magenta cast at the core. I've also boosted the micro-contrast in the 1024 x 1024 pixel image above (but not the 2048 x 2048 pixel version) on the assumption that it will be viewed from a distance sufficient to preclude pixel peeping! :) A few other tweaks, of course, but those are the headline changes.

Bob.

_________________
Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
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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PostPosted: Wed Aug 01, 2012 3:22 pm 
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My M31 shots are embarrassing compare to what you can achieved. Of course I only 30 sec exposure in the city with a DSLR.

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PostPosted: Thu Aug 02, 2012 12:16 pm 
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Well, I had to wait nearly fifty years before I was in a position to do what I'm doing now. And the image is the result of eight hours and twenty minutes of exposures, and that's not counting a few rejected subs.

I'm very happy with the final result although I'd have been happier still if I'd spotted and corrected more processing mistakes before I started the thread. But that process was helped along, particularly by good feedback on a specialist forum and, in particular, the preparation of a montage showing some of the intermediate steps. In particular the bottom left image reminded how much detail I had managed to massage out in the name of noise reduction! :oops:

So, as my final (image) post in this thread I'll show both that montage and, for easy comparison I'll repeat the end result:

    Image

    Image

The RGB image (bottom right of the montage) is what was used to colour the final image.The bottom left image is effectively my luminance channel, sans stars which were added back separately. The "H-alpha - Green/15" image was coloured and then added as a screen layer at the top of the stack.

Next task will be to start processing a four panel mosaic of the North America nebula area. The subs are all in the can but somehow the choice of 24 high definition channels of Olympic goodness keeps getting in the way! :roll: :lol:

Bob.

_________________
Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
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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