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Old 11-08-2014, 07:32 PM
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[AstroFest] Eta Carina Nebula with a small scope

Folks - I've tried this one before from LP central here and wanted to give it a go from somewhere a little darker...

This is a stack from a bunch of frames collected over a few nights from below 35 degrees altitude, down to about 20. 40x 4 minute subs at ISO1600 with the Canon 1100D attached to the WO Zenithstar 71 + reducer/flattener on EQ6. Certainly the longest set of exposures I've captured so far!

I'm not sure where to go with this one, much of the detail popped easily, but any advice/suggestions/etc appreciated as always. It's a little small because of JPEG compression working its evil ways on anything any larger
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Last edited by Camelopardalis; 11-08-2014 at 08:10 PM.
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Old 11-08-2014, 07:54 PM
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40 minute subs? Holy smokes that's long. I think the low altitude is leaving it looking a little washed out compared to what it could be if it were higher? Don't know, it's far better than anything I've ever produced!
Cheers,
Cam
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Old 11-08-2014, 08:12 PM
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my bad, 4 min subs (corrected original too)

Washed out could just be my dodgy processing I've been trying to keep the stars in check, after my Veil experience, but it wasn't very high it's true, although the sky was pretty good to fairly low down. Of course I want to try it again when it's higher, it's just a good practice object
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Old 11-08-2014, 08:50 PM
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Looks pretty decent, Dunk! It's a nice bright object so good to practice on.
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Old 11-08-2014, 08:58 PM
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Nice Eta Dunk. Did you use an LP filter on this one?
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Old 12-08-2014, 10:11 AM
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Thanks chaps! No filter, just plain old air...I've only got a UHC type and OIII. Would either of these work? Suppress the stars?

I definitely need the practice...nebulae seems to be the objects I'm struggling with at the moment, so any hints/tips/techniques you'd be free to share would greatly appreciated
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Old 12-08-2014, 11:03 AM
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The OIII would be no good for OSC. Which brand of UHC? Some are dual band with added Ha, others are not.
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Old 12-08-2014, 12:32 PM
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It's a DGM NPB.

Would the OIII not be any good for the Veil, or is it the OSC of my camera that's the problem for these wavelengths?
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Old 12-08-2014, 12:45 PM
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Quote:
Originally Posted by cometcatcher View Post
The OIII would be no good for OSC.
Why?
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Old 12-08-2014, 02:27 PM
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Why?
OIII would not make for one shot colour, which is why I worded it carefully. Sure you could use it, and add it to the green channel. But then it's no longer OSC.
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Old 12-08-2014, 02:33 PM
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Quote:
Originally Posted by Camelopardalis View Post
It's a DGM NPB.

Would the OIII not be any good for the Veil, or is it the OSC of my camera that's the problem for these wavelengths?
According to the graph I have, the DGM NPB could be used for one shot colour as it passes Ha and OIII. It looks quite narrow band. Expect long subs to compensate and funky star colour.
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Old 12-08-2014, 03:09 PM
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Here's a graphic of why it is necessary to pass OIII & Ha when taking images of the EC Nebula. I've used a Star Analyser grating to obtain a spectrum which clearly shows the strong emission of the nebula in those wavelengths. The zero order images of Eta Car and the nebula are at left, spectra to the right.

This explains the correct magenta-ish colour of EC Neb (red & blue combination), different to the bright reds of principally Ha-emitting nebulae. If you see bright red renditions of EC Neb it is either that the photographer has used Ha filters (filtering out OIII) or it has been colour-balanced or otherwise changed during processing.

Cheers -
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Old 12-08-2014, 05:54 PM
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So do you or don't you use Ha or OIII filters with an OSC ?

Thanks

Rob
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Old 12-08-2014, 06:48 PM
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Thanks Rob, that's really good to know. If you have similar spectra for other well known deep sky objects it'd be great to see them together as a resource.
Cheers,
Cam
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Old 12-08-2014, 07:29 PM
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Top stuff chaps, so I should try to get some time with my narrow pass band filter next time I'm up a bit further north then?
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Old 12-08-2014, 07:31 PM
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RobC, you can use OIII and Ha filters with an OSC camera. But... to get full colour you need to take more than one shot since each filter will produce monochrome results. So it's no longer "OSC".

Narrow band with an unmodified, uncooled DSLR also works poorly. The exposure times are much longer, so the noise can be a problem. Forget it in summer. I've seen excellent NB results with modified, cooled DSLR's however.
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Old 12-08-2014, 07:33 PM
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awesome picture Dunk!!!. gah makes me want to stake a spot out west now away from the burbs!
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Old 12-08-2014, 07:33 PM
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Quote:
Originally Posted by Camelopardalis View Post
Top stuff chaps, so I should try to get some time with my narrow pass band filter next time I'm up a bit further north then?
Dunk, I think that filter will work better from your LP home rather than a dark sky site.
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Old 12-08-2014, 10:25 PM
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Quote:
Originally Posted by LightningNZ View Post
Thanks Rob, that's really good to know. If you have similar spectra for other well known deep sky objects it'd be great to see them together as a resource.
Cheers,
Cam
Cam, here's a couple I did a while back - click to full size if necessary.

Nice image in OP by the way - well done Dunk!

Cheers -
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Old 12-08-2014, 11:36 PM
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Thanks chaps! I'm thinking it's got a bit too much red in it? What say you all?

Love the spectra Rob - keep 'em coming

Might give the filter a go at some point then How much exposure time should I be looking to add?
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