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PostPosted: Thu Dec 08, 2011 6:36 pm 
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Hi folks,

What do you think?
    Image
The full sized version (all 3.8MB of it) can be seen at 100% by clicking the image.

I've posted some preliminary versions of this image elsewhere but as this is the finished article I decided to promote it into its own thread. The North America nebula, slightly above and to the left of the image center, is fairly obvious by its shape. Immediately to its right is the Pelican Nebula and about two thirds of the way down the right hand edge of the image is the Gamma Cygni Nebula complex around the star Sadr. The brightest star in the field is Deneb in the constellation of Cygnus.

The image was captured with a fairly cheap 165mm f/2.8 Pentax medium format lens but the dedicated CCD camera behind that lens, an FLI ML16803, was far from cheap! The nebulosity in the image is all from Hydrogen alpha emissions. That is about as far into the red end of the spectrum as the eye can see. That left me with a problem as if I had shown all the Hα as pure deep red I would, IMHO, have ended up with a difficult to see image. Nature comes to the rescue as Hα is usually accompanied by a blueish Hβ line at about one third the intensity so for the image above I added in some blue and then, purely for aesthetic reasons, also added in some green to the fainter and brighter regions (screenshot) to give a whiter appearance. False colour narrowband images aren't at all uncommon these days so hopefully my choices are acceptable as I'm not representing the nebulosity to be anything other than Hα.

The stars in the image are actually from a totally different set of RGB images captured on the same evening. The Hα image had it's stars removed and the stars from the RGB image were added in. That was done not only to allow some natural star colour to come through but also to avoid the rather selective sampling of stars when imaging in Hα light.

I hope you like the final result but if not then please feel free to offer advice. This is my very first "finished" Hα plus RGB photo and there are so many decisions to be made during processing that I'm sure there's room for improvement.

Bob.

P.S. Hα was from 5 x 1000 second exposures, each of the RGB images was from 3 x 200 second exposures.

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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: Thu Dec 08, 2011 7:37 pm 
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Only a quick look as my internet expires in 5 mins. Nice detail, not sure about the colour palette but it could be my work laptop as screen is rather horrible on it. Will have to have a better look when I get home tomorrow.

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PostPosted: Thu Dec 08, 2011 10:27 pm 
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Great work Bob. Technically it's excellent and I admire the work you've put in.

I agree the colour is a tricky one though. Aesthetically it does feel a bit too 'red', but short of exploding a few stars with the right chemical composition you've gotta work with what the Universe has given you...


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PostPosted: Fri Dec 09, 2011 11:24 am 
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"Exploding a few stars" - I like it! :twisted:

Thanks for the comments - I still don't have a clear idea of where, if anywhere, I'd like to take the colour but I realised this morning that I had failed to take advantage of Noel Carboni's "Local Contrast Enhancement" PhotoShop action to bring out a little more detail in the nebulosity. With that applied to the "No Stars" image and with a few further tweaks as seemed appropriate this morning here's the final "final" version. As before the full sized JPEG is available by clicking the image.
    Image
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: Sat Dec 10, 2011 11:38 am 
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Hi Gordon, Hi popo,

I applied "+6" to the tint using PhotoShop's Hue/Saturation tool to reduce the magenta in favour of a redder look. I think that improves the image - do you agree?

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: Sat Dec 10, 2011 11:51 am 
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It looks a lot better on my home monitor than my work laptop! I think the redder colour is more pleasing to me too. Magenta felt out of place for me. I do wonder if the nebulosity is too "thick" in a way, but I'm probably getting far too over-analytical on what it should look like, based on other images seen in the past which may have had very different processing.

Side note: when checking the colour, I did the FF vs Chrome comparison. I think in this case FF looks right, and in Chrome it looks over-saturated and contrasty.

Too many variables!

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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 Dec 11, 2011 12:40 pm 
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Hi folks,

Yesterday I became aware that there could well be gamut issues with the image above for some monitors. I also needed to develop a better set of curves to allow the monochrome H-alpha image to be colourised without introducing the original magenta tint. Here's today's final (final "final") offering:
    Image
How does that look?

The full sized version (4096 x 4096 pixels, 5MB) is available by clicking the image.

I tackled the gamut issue by reducing the slope of the red curve but still kept it straight. The magenta issue was resolved by boosting the mid-tone green. I also took the opportunity to boost both green and blue highlights to give a whiter appearance for the very brightest parts of the nebula, something which I think also helps bring out more detail. Here's what the curves look like:
    Image
Thanks for bearing with me and following my efforts to get the colour where I want it. As ever, any comments are welcome. 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: Mon Dec 12, 2011 8:29 am 
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I agree with popo Bob, and think the redder version looks better. There's also what looks like a slightly greater tonal range in this last one.

PS - I'm watching with an Eizo CG210.


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PostPosted: Mon Dec 12, 2011 10:35 am 
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Thanks, Gordon. It's good to know I'm on the right track. I have a revitalised and deep respect for the guys and gals out there who routinely make their deep sky images look so beautiful. It's harder than I thought!

I've also been getting some advice over at the Cloudy Nights forum and this morning I corrected some clipping at the low end of the histogram and applied an "S" curve to the shadows/midtones. That has recovered some of the fainter nebulosity I lost while agonising about colour. But then I decided to start over with the monochrome H-alpha image and apply PhotoShop's "Shadows/Highlights.." adjustment before colourisation and then repeated the workflow as before. Here's the result:
    Image
As ever the full res (4096 x 4096 pixel, 5MB) version can be seen by clicking the image.

Update: This is actually "tomorrow's" image! I posted today's image this morning, had the idea to use Shadows/Highlights and so did tomorrow's image this afternoon and just updated the links. :lol:

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 Dec 12, 2011 6:21 pm 
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Hi folks,

From Douglas Adams' "Hitchhiker's Guide to the Galaxy":
    Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is.
    I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space.
And if you are in any doubt about how big space really is, the time it would take a beam of light to cross from one side of the nebulosity (picture above) to the other is, if I've got my sums right and assuming about 500 light years, around 32 million times longer than it takes light to reach us from the Sun. And if the distance from the Sun to the Earth is a bit of a mystery then that same beam of light that would take just over eight minutes to get to us from the Sun would cross the Atlantic from London to New York (assuming a flat Earth!) in about 1/50th of a second.

How far would the distance from the Sun to Proxima Centauri, the nearest star to the Sun, look if they were about as far away as the North America nebula pictured above? About half the width of the black border! :shock:

Douglas Adam's had it about right! "Space is big..."

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 Oct 31, 2012 6:38 pm 
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Hi folks,

Almost a year on I decided to look at the original data today to see how my processing skills have evolved. Here's the result:

    Image

      NCG7000 to IC1318

I've chosen a less controversial colour scheme for the Hα this time around as a bit of an experiment: the downside is that the brighter Hα regions display less prominently. The other major changes are better calibration frames and brighter stars.

Update: For comparison here's a version where I use my normal "Ha to Colour" Photoshop layer. Less of the magenta and I let the highlights wash more towards white. Definitely "false colour" but I think it allows the eye to pick out more detail.

Image

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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