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Old 28-08-2009, 04:28 PM
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g__day (Matthew)
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Why is NGC 2070 green in DSLR's when Triffid has correct colours?

I'm puzzled why M16 and M20 seem to have the expected colours (on an unmodified Canon 400D) but the Tarantula NGC 2070 is a real Jade colour (through a C9.25 and Hutech light pollution filter)

Can anyone please explain why and the best way to regain colour fidelity in image processing? Particularly I'm confused why the colour balancing I use in CS4 or Deep Sky Stacker (align the Histograms) doesn't come close to giving me the colours serious amateurs get on this DSO but for my other regular targets color fidelity is fine?

Many thanks,


Attached are two sample piccys 49 minutes of data C9.25 at F10 *5 shots combnined). The first is "captured colour" the second is reprocessed to strech and amplify the red.
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Click for full-size image (Tarantula 4200 secs v02 smaller.jpg)
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Click for full-size image (Tarantula 4200 secs v05 smaller.jpg)
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Last edited by g__day; 28-08-2009 at 09:19 PM.
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Old 28-08-2009, 05:39 PM
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Octane (Humayun)
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My understanding is that this region emits a lot of oxygen, hence the green.

I could be wrong.

My first attempt at photographing that region through a 105mm triplet and an unmodified 350D came out entirely blue with the slightest magenta portions.

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Old 28-08-2009, 07:29 PM
Alchemy (Clive)
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i put this on a reply to the tarantula image from peter... relevant to here

Hydrogen alpha emmissions are in the red end of town, your oxygen 111 are in the blue/green, both being emmisions, your reflection nebs are scattered blue light and some of the darker dust will be into the browns.

the colors of various objects will depend on the type of light coming from them combined with the cameras ability to handle those same wavelengths.

An unmodded DSLR does not have a high response to the red Ha so its diminished , if you shoot the cats paw, it really only emits in the Ha so even with DSLR you will get reds (not a lot) the same goes for the horsehead,

however some objects (in this case we have the tarantula) there is a high amount of the O3 possibly also some reflection in there too, in an unmodded camera this will swamp the little red you have, and voila a blue tarantula.

Some objects have a combination of both and as a result red plus blue looks purplish, you will find this in say the Carinae Nebula.

there is no wrong or right, its just what your camera percieves. Insects see well into the ultra violet and probably see everything different to us completely. there has been much perhaps condescending talk about unmodded cameras. i personally dont care, blue/red whatever its just that part of the spectrum you have captured.

enjoy thats what counts.

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Old 28-08-2009, 09:01 PM
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g__day (Matthew)
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Thanks for the excellent diagnosis of what I am seeing - that certainly makes sense.

So on a camera that isn't red Ha sensitive, is the only processing treatment to correct for a lack of sensitivity to red (and maintains any colour fidelity) and simply boost the signal? I could always just go into curves and simply boost the Red channel - but that seems kludgy - and I'm sure brings its own problems with it. I guess its a no win situation - if your image simply isn't sensitive to Ha then it doesn't have the data - and you can't fake it. You can't porocess in what you don't have right?

So is there a better way to treat the data you do have?


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