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WIP - Trifid Nebula ( M20, NGC 6154 )


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Updated:  new processed version ( no new data ) - 9th July

5962ae4877801_TrifidNebula.thumb.jpg.e22346c0f7c4aab11718fefbf615262d.jpg

( please click / tap on image to see larger / sharper )

Still needs work but I do quite like the way the dark clouds are showing up against the bright nebula and I think the star colour is fairly close to accurate ( albeit that the saturation is too high ).

.........

Just a work-in-progress version ... 

This is a central crop ( around 1/3 width ) of the original image and I am still trying to find the best way to process it ( this one has way too many problems; not least of which is the overblown stars and weird highlight artefacts on a few of the stars...).  I have processed 12 stop HDR images before successfully but this one is proving very challenging.  

Anyway, I am sharing it now because the best results I have had so far involve stretching an extracted intensity image and then applying this to the RGB image to effectively stretch the colour image without any colour shifts and I was suprised that it produced this highly saturated image.  That is, the image below has not had any manual adjustment to the saturation or any tweaks to colour balance.

Summary of workflow:

- Calibration ( master bias/flats, no darks )
- de-bayer
- alignment 

then per set of images ( 12 sets in total from 1/8sec to 240 sec all at ISO800 - around 10 each for short exposures and 26 of the 240s long subs)
- integration 
- DBE to obtain the background ( throw away the corrected image - just keep the background )
- Pixelmath to find the minimum of the background image and use this to produce an average Light Pollution image
- Subtract the LP from the integrated image

- HDRCompostion of the 12 integrated LP corrected images to create masks - throw away HDR image ( not usable for some reason - terrible colour shifts )
- Pixelmath to combine images with masks to produce an HDR image ( 64bit) with around 32bits of dynamic range
- Extract CIE-L as new layer
- Multiple interations of Maskedstretch of CIE-L image to produce a fully stretched image
-Pixelmath to scale RGB image using CIE-L inage level information
- some level tweaks ( curves and histogram )
 

5958d37fa8313_TrifidNebula-large-Workinprogress-170702-byMikeODay.thumb.jpg.b270cfb584a759e618474b6d43e79b79.jpg

mmm, still not happy - I need to keep experimenting ...

 

Anyway, as I said, I am very suprised that the workflow produced such a saturated image with ( I think ) quite good colour balance.  Equally I was suprised to see such a range of star colours from deep orange through gold to white and blue - all without having to spend ages tweaking colour balance as I usually have to :)  .

( note: camera is an unmodified DSLR ( Nikon D5300 ) so HA regions are not so red )

 

Edited by mike005
new processed version ( no new data )
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1 hour ago, ollypenrice said:

It's good, but are you dead sure about focus? Tricky at very low altitudes...

Olly

Cheers Olly.  Not so low for me - I'm at around 33.7 deg South down here near Sydney.

Focus could be off - often a problem for me.

IMG_0867.JPG.e29dd267717334d6d97e692638573809.JPG

Hard to tell from this image due to the bloating of the stars - no double spikes thought so fairly close for me :).

 I'll check one of the subs.

 

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16 hours ago, ollypenrice said:

It's good, but are you dead sure about focus? Tricky at very low altitudes...

Olly

Hi Olly

I checked the integrated 240s image and it is a bit soft and perhaps a tad out of focus but I think the main problem might be poor seeing causing the stars to bloat; what do you think ?

bandw.thumb.jpg.97a1d64e15fc264305bc3f366ec046d9.jpg

HDR image ( CIE-L ) stretched and deconvolution applied

 

IMG_0868.thumb.JPG.db0b5cd0d8f5e7d695b72803e1ea5fd1.JPG

100% crop of linear ( unstretched ) integrated 240s image  ( no sharpening/deconvolution )

15x enlargement of idicated star below

595a27676093d_singlestar.jpg.28dd8e11a00730c8da3faaf06e1bff12.jpg

 

Edited by mike005
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The enlarged star above looks red on one side and blue on the other.  Is this not atmospheric dispersion since the target is low?  I know this was an OSC, but it is worth aligning each colour channel separately?

 

Edited by AKB
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18 minutes ago, AKB said:

The enlarged star above looks red on one side and blue on this other.  Is this not atmospheric dispersion since the target is low?  I know this was an OSC, but it is worth aligning each colour channel separately?

 

I'm sure you are correct - my stars always suffer from this effect to a lesser or greater extent; even when the target is quite high.  In this case I started capturing subs when  the Trifid nebula was about 1hr past the Meridian and around 70 odd degrees above the horizon (down here near Sydney) and was about 35deg lower at the end of the session.  

Do you notice much improvement by separately aligning the channels?  I did try this once in the past and the offsets between the channels was less than a pixel so I have not done it since.  I'll have a look at the weekend with some of the subs from late in this past session and see what happens.

Cheers

Mike

 

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22 minutes ago, mike005 said:

Do you notice much improvement by separately aligning the channels?

I've found that this has helped a lot for planetary targets, but haven't actually tried imaging DSOs or anything else too low.

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I agree that focus is a bit soft--which is magnified by cropping.  I would like to see the natural FOV--there is some nebulosity cropped out I think.  But all said, a nice image--keep collecting data and drop inferior subs as better ones are obtained.  You'll get there.

Rodd

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20 hours ago, AKB said:

I've found that this has helped a lot for planetary targets, but haven't actually tried imaging DSOs or anything else too low.

 

18 hours ago, Rodd said:

I agree that focus is a bit soft--which is magnified by cropping.  I would like to see the natural FOV--there is some nebulosity cropped out I think.  But all said, a nice image--keep collecting data and drop inferior subs as better ones are obtained.  You'll get there.

Rodd

Thanks Guys, much appreciated.

Better processing will help with the sharpness a bit I think ( or at least I should be able to tighten up the stars a bit if I reduce the amount of induced bloating ).  Not much I can do about the focus going forward - I already focus on the diffraction spikes and the best I can usually achieve is to ensure that there are no obvious double spikes.  I will check it again though when the moon goes away in a couple of weeks. 

I am hopeful that I can improve the tracking when I can install my new mount ( EQ8 ) - just waiting for the adapter plate to arrive for my pier.  When I have got it set up I intend to play again with the focuser tilt ( this is still not right ) and double check collimation.

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Updated:  new processed version ( no new data ) - 9th July

5962df5cb5adc_TrifidNebula.thumb.jpg.add98bb665dfec1525a19a77ad2ec597.jpg

( please click / tap on image to see larger / sharper )

Still needs work but I do quite like the way the dark clouds are showing up against the bright nebula and I think the star colour is fairly close to accurate ( albeit that the saturation is too high ).

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I was unsure about the bright "red" star near the centre left of the image - it looks "too red", so I looked it up...

IMG_0932.thumb.JPG.99b47bd929f9b4e6f0e65efa6ceba506.JPG

Using AladinLite I found the following star at that location:  " V* V1948 Sgr " or  " 2MASS J18021769-2240093 " that according to SIMBAD is a Carbon star

IMG_0934.PNG.afc95913946420fd3680192a8b5a5d46.PNG

And from WIKIPEDIA a Carbon star is:

A carbon star is typically an asymptotic giant branch star, a luminous red giant, whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds, giving the star a "sooty" atmosphere and a strikingly ruby red appearance. "
 

So the saturation may be too high but the deep red/orange may be about right.

 
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Still playing about ...

Two new versions ( just quick adjustments ). 

A couple of even more colourful version for those ( including my wife ) who prefer the bright colourful versions of astro photos ...

IMG_0938.thumb.JPG.c87cac571f7ebe8926d53eb88e18df5a.JPG

IMG_0940.thumb.JPG.782ac43db31c8d6ce33112d00b0b0589.JPG

And a quick desaturated version ( I will have to wait until the weekend before I will have the time to go back a few steps to reduce the saturation properly )...

IMG_0939.thumb.JPG.ca12b651b6eda7ab12b3bd60a69117fe.JPG

Edited by mike005
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A nice image Mike.  Perhaps a reduction of brightness in the nebula may bring out some fine details.  Some areas are nearly white.  If you drop them down a bit the dark structures will start to pop.  Just a thought.

Rodd

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On 11/07/2017 at 02:57, Rodd said:

A nice image Mike.  Perhaps a reduction of brightness in the nebula may bring out some fine details.  Some areas are nearly white.  If you drop them down a bit the dark structures will start to pop.  Just a thought.

Rodd

 

On 15/07/2017 at 20:52, PatrickGilliland said:

Nice image Mike - I wonder if more range in the contrast would show some more detail.

Thanks guys.

Yes I need to get back to this and look at the bright areas ...

This one is definitely a challenge with exposures ranging over 12 stops from 1/8sec to 240sec.

Cheers

Mike

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