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 Post subject: Rubies are Red
PostPosted: Sun Oct 09, 2011 2:32 pm 
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Hi folks,

Simple question: Which area or areas in the image below look most like a deep red ruby colour to you?
    Image
I've added an indication of x and y coordinates so you can share your choice. Mine would be either x=8 and y=3 or x=3 and y=4. As you can see, I'm not going for great precision here but I might get an indication of how most monitors and the eyeballs viewing them are set up.

The question arose in my mind after having had a first look through my new narrowband Hα filter which just lets light through at a wavelength of around 656 nm. That is a very deep red and my Mark 1 eyeballs tell me that there isn't a computer monitor out there that any of us are likely to own that can actually reproduce that colour. The nearest colour that sprang to mind was "deep red ruby", hence the question.

As for the chart above, I produced it for future reference to help in picking colours for reproducing nebulosity from a range of narrowband data. It's not scientific in any shape or form having been produced by a bit of freehand gradient drawing but it does contain most of my intended future palette. Maybe I should have aimed for more yellow but yellow in large quantities isn't a colour I find particularly attractive in most astro-photographs. If yellow appears as a result of mixing an RGB palette then fine but I hope to avoid starting off with large gobs of it! :twisted:

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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 Post subject:
PostPosted: Sun Oct 09, 2011 2:52 pm 
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I think I'd have to go for about 9,2, calibrated against my H-a filter. What my imagination would call deep ruby would be nearer 9,1 I think.

Side note: tilting my filter slightly changes the colour between an orangey-scarlet to a red with hint of purple so I had to look through it carefully keeping it perpendicular.

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
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3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


Last edited by popo on Sun Oct 09, 2011 2:53 pm, edited 1 time in total.

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 Post subject:
PostPosted: Sun Oct 09, 2011 2:53 pm 
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X9 Y3 I think.

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 Post subject:
PostPosted: Sun Oct 09, 2011 2:57 pm 
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Further note: the old chestnut of browser colour management came in again. The earlier score was for firefox, and loading it in chrome I get a much more saturated image. I wouldn't change the score though but would put a +/-1 tolerance on it.

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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
Tinies: Sony HX9V.


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 Post subject:
PostPosted: Sun Oct 09, 2011 3:18 pm 
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.
Thanks guys for the immediate responses. The right hand edge of the picker is pure red but none of us want to go there. We are all opting for areas with mostly red but also with a significant (15 to 20%) blue and pretty much zero green.

Obviously in nature the deep red of Hα has no blue component at all but it seems that the limitations of the sRGB colour space, which can't natively get to the Hα colour, mean the eye has to be fooled and that is done by adding a little blue.

But it's a small sample so far so, for anyone who would like to, please add your own choice of x and y for that deep red ruby colour... 8)
    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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