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Old 06-12-2016, 07:43 PM
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Question Opinion: what hue should OIII be?

Folks,

I've read conflicting opinions on the interweb and not all filters are made equal, so I put it out there to you...with broadband CCD imaging of an emission nebula like the Tarantula, what colours should we see?

Cheers,
Dunk
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Old 06-12-2016, 08:16 PM
glend (Glen)
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Dunk my personal opinion is that broadband images of the Tarantula should be colour balanced as heavily turquoise. Certainly if you shoot it in narrowband the Oiii will result in a bias towards turquoise naturally based on the location of the spectral lines.

Last edited by glend; 06-12-2016 at 08:32 PM.
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Old 06-12-2016, 08:36 PM
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Merlin66 (Ken)
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IMHO it really depends of the bandpass of the OIII filter.... I feel it's a teal colour....
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Old 06-12-2016, 08:54 PM
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Shooting in NB?
Colours are Dealers choice, anything you want it to
That said, O3 lies around 500nm somewhat near blue/green.
Cheers
Andy
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Old 06-12-2016, 09:14 PM
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http://encycolorpedia.com/00b8e0 (this colour has a wavelength of approx 500nm)

... but as Andy says you can do what you want in NB
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Old 06-12-2016, 09:50 PM
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This is more broadband I'm interested in, i.e. RGB. I collected some data at the weekend with my ZWO filter set and when I blend the channels the Tarantula comes out a nice shade of green

Does anyone know of a reference point that should be strong OIII? I took a bunch of subs in G and B of the same exposure time, so it'd be interesting to compare.
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Old 06-12-2016, 10:49 PM
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Without filter the Tarantula is bluish:

http://skysurfer.eu/skypics1/NGC2070...217-8x2min.jpg

and another picture I took with a UHC-S clipin :

http://skysurfer.eu/skypics1/LMC-16x4min-20160301.jpg

which is more red (due to Halpha pushing which is alsp passed by a UHC-S but NOT with OIII). I took the puctures with a Canon 6d.

The natural color of an OIII is bluish green, so color balance has to be adapted, hence my more reddish Tarantula.
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Old 07-12-2016, 11:40 AM
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Nice pics, thanks

I guess it's one of those things that could vary slightly due to the QE of different cameras and transmittance of the filters

Looking at the bandpass profile of the ZWO filters I'm using, OIII is squarely in the green filter, which explains why it's strongly green. Looking at my exposures, the green:blue is about 2:1.

Any suggestions on a nice set of RGB filters that would give me good ol' teal/turquoise/insert shade here* ? Oh, and inexpensive
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Old 07-12-2016, 11:56 AM
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Quote:
Originally Posted by Camelopardalis View Post
Any suggestions on a nice set of RGB filters that would give me good ol' teal/turquoise/insert shade here* ? Oh, and inexpensive
Use the ColorMask script for free, Dunk

I'm only half joking. You'll never get perfectly accurate colour from any set of filters because of variations in sensor QE, atmospheric extinction, etc. You're better off honing your colour calibration technique.

Cheers,
Rick.
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Old 07-12-2016, 12:41 PM
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Great stuff Rick, thanks downloaded and installed

Appreciate what you say about the filters, but...makes me wonder if a filter set where G and B overlapped for OIII would give richer signal, or conversely, overblow it.
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Old 07-12-2016, 01:23 PM
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So, a quick stab at shifting the green

The purple should be the areas where the OIII and Ha are mixing. I'd expect this to differ from an unmodded DSLR which wouldn't let as much Ha through.

Still need to work at it a little more I think, but it's a start...
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Old 07-12-2016, 02:03 PM
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here is what an o3 filter (8.5nm) looks like on a (colour) dslr.
https://www.flickr.com/photos/80336656@N07/16601437552/

looking at the G and B channels, the signal is WAY stronger in the G - but I'm not sure if that's because it has double the pixels in the bayer matrix... - either way its probably 5x plus richer in G (total guess)

not sure that helps at all. of course its rare to have o3 just by itself so a light pollution filter/osc will likely give a different hue.

Last edited by rustigsmed; 07-12-2016 at 02:17 PM.
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Old 07-12-2016, 02:09 PM
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Quote:
Originally Posted by Camelopardalis View Post
Appreciate what you say about the filters, but...makes me wonder if a filter set where G and B overlapped for OIII would give richer signal, or conversely, overblow it.
The ZWO filters do look pretty crappy in that regard. The Astrodon filters have a much nicer overlap at 500nm. I'll withdraw my previous comment.
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Old 07-12-2016, 07:36 PM
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Quote:
Originally Posted by rustigsmed View Post
here is what an o3 filter (8.5nm) looks like on a (colour) dslr.
https://www.flickr.com/photos/80336656@N07/16601437552/

looking at the G and B channels, the signal is WAY stronger in the G - but I'm not sure if that's because it has double the pixels in the bayer matrix... - either way its probably 5x plus richer in G (total guess)

not sure that helps at all. of course its rare to have o3 just by itself so a light pollution filter/osc will likely give a different hue.
Thanks Russ! That's a pretty interesting result. Can't wait for Eta Carinae to get higher in the sky.

It hadn't occurred to me to stick the filter wheel in front of a DSLR...I'll have to give that a try

Quote:
Originally Posted by RickS View Post
The ZWO filters do look pretty crappy in that regard. The Astrodon filters have a much nicer overlap at 500nm. I'll withdraw my previous comment.
From what I've found so far, the Baader CCD and Astronomik Deep Sky both overlap at 500nm. The Astrodons apparently are too tall to fit in the ZWO filter wheel.
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Old 08-12-2016, 08:21 AM
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Ha is RED, OIII is yellow and SII is orange.

This week anyway!!!!
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Old 08-12-2016, 10:32 AM
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Old 09-12-2016, 01:30 PM
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Don't know if this helps... Enlarge to full size.

Cheers -
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Old 09-12-2016, 05:30 PM
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Thanks Rob, that's a great reference
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