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 Post subject: Pick a colour...
PostPosted: Fri Jan 20, 2012 12:56 pm 
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Getting a little tiered of looking at the redness of H-alpha only images, and my fail at mixing it with RGB data, I just ordered SII and OIII for some false colour action when they arrive. Skies allowing.

But I got thinking... is there a relationship between H-alpha and H-beta strengths? I know Hb emission is weaker than Ha, but for bayer pattern sensor imaging, Hb is located in a more favourable spectral location where it is moderately sensitive to both blue and green channels. The potential for increased spatial resolution and more usefully active sensors I think would offset the lower output of the Hb emission, although I'm not sure if it is a net gain. So could I use Hb as a substitute for Ha, or is it something different enough in its own right to explore?

I'd even consider throwing some Nitrogen into the mix but the filters for that seem a bit more... on a side note, Ha, SII and OIII are the only narrowband filters offered in EOS-Clip. If I were to try something more exotic I'd have to significantly revise my configuration.

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PostPosted: Fri Jan 20, 2012 1:36 pm 
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Hi popo,

Off the top of my head the theoretical ratio of Hα to Hβ is about three to one. It's out there on Google somewhere but bear in mind that the Hβ is more prone to scattering by intervening dust.

Here's my current starting point for conversion of a monochrome image just after selecting RGB mode:
    Image
I find I still have to fine tune the curves for some images but this crop pretty much covers the whole tonal range and, from memory, was pretty much using that set of curves straight out of the tin.:
    Image
My initial idea was to add blue to simulate Hβ but the without the green I found the result unpalatable so, as Hβ isn't too blue, I rationalised the addition of the green. The idea behind equal red, green and blue for the lowest signal was a rather bizarre attempt to mimic the eye's lack of colour vision at low intensity but I'm finding that the effect doesn't work too well so I think I may ditch it in the future. But I do like adding more green and blue at high intensity as I find the whiter look more intuitive when things get really bright. I tend to go my own way on this so, again, if you Google you should find plenty of more conventional recipes.

Bob.

P.S. Looking forward to your results with the new filters. I have a feeling that the recipe above won't suit for multiple narrowband input.

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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: Fri Jan 20, 2012 5:57 pm 
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I was thinking of getting more spectrum, as opposed to synthesising it. For whatever reason my PixInsight output has white stars with only a H-alpha filter used, presumably from whatever little sensitivity is remaining in the green and blue channels.

On that note, H-beta and OIII seem to sit between green and blue as far as typical bayer colour filters are concerned, so it sounds reasonable you'd need similar quantities of those if that is what you're trying to imitate.

Ooh, interesting thought. One thing I didn't like about H-alpha with a DSLR sensor is only 1/4 of the sensor (red) is significantly sensitive. If I use H-beta, I'd get 3/4 (2 green 1 blue) of the sensor producing significant output, but from 1/3 the source strength. Referencing here as indicative of Canon colour filter array characteristics, for a modified 50D, we see Ha at ~658nm has a pixel QE of about 0.25. Hb at around 486nm is... about 0.25 for both green and blue! Roughly speaking, no net gain in sensitivity per area, although if I can expose long enough through the noise I could get the extra spatial resolution using Hb than only using Ha would get me.

Which is great in theory but not easily tested by me since I can't easily use such a filter.

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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
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 Post subject:
PostPosted: Sat Jan 21, 2012 9:50 am 
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Ah, sorry. I misunderstood the question. OIII and NII are next on my list but probably not until the summer. 8)

Update: Here's a link I bookmarked some while ago discussing combining Ha and OIII images. Obviously I've yet to test it.

And here is a thread I bookmarked a while ago because I liked the effect.

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: Tue Jan 24, 2012 12:43 pm 
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Just received the narrowband filters for imaging. So you can guarantee there wont be clear skies at night for a long time now.

On a positive note and another look, I did see there does appear to be a H-beta filter in EOS clip size so I could get that... maybe later. Spent enough on these two as it is...

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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
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PostPosted: Thu Jan 26, 2012 10:07 pm 
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This'll be... interesting.

Given the sky is clear-ish right now I had to try out the new filters. The OIII was giving me trouble on the modified 450D. I was getting significant halos, which I think is IR contamination as the filter I got wasn't a "CCD" version. Works fine on an unmodified 600D so I grabbed 17x2 minutes with that which PixInsight is crunching now.

I've put in the SII filter on the 450D now and will see what that gives. It is VERY dark. Can't see Sirius through it. Jupiter is very faint too but bright enough to use for focus.

Hope PixInsight has a good resize option - until I find it and work out how to use it, have just exported to TIF, resize in PS, and re-import to PixInsight.

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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: Thu Jan 26, 2012 10:56 pm 
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Hi popo,

I think PixInsight's StarAlignment process will automatically resize. The reference image choice would probably be the lowest resolution. I haven't tried this though.

It was raining here with showers forecast so I took the night off.

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: Thu Jan 26, 2012 11:08 pm 
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I've stopped early as condensation was getting over everything, although I didn't stop until that included the lens front.

Image
Here' a quick 1st process of the OIII and partial SII data from tonight, combined with Ha previously. I did a straight add of the three sets of data so it's kinda real colour, although I can't claim the channels are balanced correctly. The OIII definitely helps as the extra resolution from the ~75% sensor coverage could be easily seen compared to the Ha or SII data. (note - seems Picasa hosting jpeg recompression has knocked a lot of detail out of this - I might try an alternate host later)

Next trick - try to figure out how to do a false colour combination - might have to give up on doing it in PixInsight and just manually do it externally.

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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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PostPosted: Thu Jan 26, 2012 11:45 pm 
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Image
Kinda figured how to do a false colour composition in PixInsight. Again I don't think it is optimised due to the channel levels, but I tinkered with it some more in photoshop after and got the above.

This is in "Hubble palette", that is R=SII, G=Ha, B=OIII. The SII and OIII are more visible around the centre of the Rosette, with the Ha expanding further. I don't know if that is the case or just a case of relative sensitivities.

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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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PostPosted: Fri Jan 27, 2012 12:11 am 
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Still Hubble palette. Went back, treated the channels separately before recombination. This happened.

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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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PostPosted: Fri Jan 27, 2012 12:26 am 
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Excellent stuff. You must be chuffed to bits. 8) 8) 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: Fri Jan 27, 2012 12:40 am 
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Kinda, but it doesn't help me resist looking at a fat scope and cooled CCDs!

Still lots to learn about processing. Also the above images didn't have all the SII data I got from tonight so possibly I can get the noise down a little more.

_________________
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: Re: Pick a colour...
PostPosted: Sun Aug 12, 2012 9:26 pm 
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Image

Another revisit of this processing wise. I think I'm dialing in on the look of actual Hubble images now...

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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: Re: Pick a colour...
PostPosted: Tue Aug 14, 2012 3:13 am 
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Have to say interesting stuff and dedication for this type of shooting.


Cheers

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