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PhotoGav

M27 - The Dumbbell Nebula

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This data set has been sitting on my laptop since capture back in July last year, waiting patiently for me to pluck up the courage and find the time to try and turn it into a presentable image. Well, that has finally happened over the last few days and here is my latest rendition of that popular planetary nebula astrophotography target some 1,400 light years away in Vulpecula. I know, it's a bit odd posting a summer target in the depths of winter, but at least it helps to remind us that the sky can be clear sometimes!

 

M27-HaOIIIRGB-07-Flat.thumb.png.8d6b9ebe97fba216014fd4f303a4019b.png

 

Technical Details

Celestron EdgeHD 8" on a Mesu 200 and QSI 683-WSG8 with 31mm Astrodon Filters (5nm narrowband)

RGB = 18 x 300s each
Ha = 26 x 1800s
OIII = 28 x 1800s
Total Integration = 31 hours 30 minutes

I changed my usual processing workflow with this image and gave Starnet++ a try. All the calibration and stacking was done in Astro Pixel Processor, along with the RGB combination. I saved out the RGB, Ha and OIII stacks, each with the Digital Development from APP. (I do love APP ever more, especially having had a long, detailed and generally wonderful chat with its creator, Mabula Haverkamp, at AstroFest this year - what a totally lovely chap!). I took everything into PhotoShop and did a few bits and bobs. I struggled to successfully combine the narrowband and broadband data - it just wouldn't fit together nicely. So, a brainwave struck me and I wondered whether that Starnet thing I had read about might just be the answer. Once I had sussed out how the heck to get it to work (thanks to a post from Andy on IceInSpace for the very useful notes!) I let it strip away the stars from the Ha and OIII images. I then combined the two starless images as a bi-colour Ha/OIII/OIII in PhotoShop and tried adding that to the RGB starfield using Screen blending mode. Wow, that was far more the kind of thing that I was looking for! I then did the few polishing techniques to arrive at this final version.

I am a bit disappointed that there isn't more of the outer halo of material visible in the image, but I've pushed the data as far as I am happy to go and that is as much as it is willing to yield to me. It has a mysterious outer glow and that is OK, but all in all, an insufficiently dark sky coupled with a slow (f10) telescope has left that glowing material hidden in space. Nevermind, there's always next time... if we ever get to see the night sky again that is - this incessant cloud is now really getting tedious. It's scuppering my current attempt at a four pane mosaic of the Spaghetti Nebula! (If I ever get enought data for that one I will definitely be trying this starless narrowband processing approach with it).

Clear skies to you all and I hope you like this image.

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1 minute ago, Laurin Dave said:

Very nice Gav and an interesting processing method which I shall take a look at

Dave

Thanks Dave. The technique allows a good stretch of the Nebula without killing the stars. It’s basically what the Finnish guy, JP Metsavainio (aka AstroAnarchy), was doing years ago, I just could never suss out how he was doing it! Starnet seems to be an easy solution. It’s not perfect by any means and I needed to tidy up some of the brighter star removal areas to avoid weird artefacts. Definitely worth a play though. 

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Very nice indeed. I've also been using Starnet on my images but using blend mode lighten to add the stars back in. Must give screen a go for comparison.

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4 minutes ago, Allinthehead said:

Very nice indeed. I've also been using Starnet on my images but using blend mode lighten to add the stars back in. Must give screen a go for comparison.

Thanks Richard. I ended up with the Nebula on the layer above the stars so used Screen mode. If the layers were the other way round I guess Lighten mode would bring the stars in. I wonder which works better?

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Yes, that is a very nice Dumbbell! So much details in the cetral areas.

I also have to learn to use Starnet one day - there is no PI plugin version that I can use on my Mac and I have so far not figured out how I get the stand alone version to run.

You could try the "Equalize method" that Olly @ollypenrice invented and described here a few months ago to tease out more of the outer shell. I had a crude go at it with your posted 8 bit image to see if it could work (hope you do not mind and it would be better done on the 16 bit of course). I first used the Equalize adjustment (Image -> Adjustments -> Equalize). I then did a rather strong NR and some gaussian blur on it and then added it as a layer to the original image, just letting about 5% through with the slider, and finally suppressed the brightened background a bit with a curve. There was quite a bit more shell to be seen.

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Thank you Göran, I will have a go at teasing out more from the outer shell with the Equalize method. In fact, you make me think of the Screen Mask Invert technique that I forgot to try - I was so engrossed in the Starnet thing!

As for how to get the standalone Starnet version to work on the Mac, here's the method I used:

1. Download the latest version of Starnet for Mac OS from here: https://sourceforge.net/projects/starnet/files/v1.1/StarNet_MacOS.zip/download

2. Unzip the folder and place it on your Desktop

3. Save the image that you want to make starless as a 16 bit mono or RGB .tif file

4. Place the file in the Starnet folder on your desktop

5. Open Terminal and navigate to the Starnet folder (you can do this by pasting - cd ~/Desktop/StarNet_MacOS - into Terminal and hitting Enter)

6. Open in Text Editor either the file 'run_mono_starnet.sh' or 'run_rgb_starnet.sh' depending on whether you are working with a mono or RGB file and edit the filenames in there to be the filename of the file that you want to make starless

7. Drag either 'run_mono_starnet.sh' or 'run_rgb_starnet.sh' onto the Terminal window and you should see the path of the the file appear

8. Make sure that Terminal is the uppermost window and hit enter - Program will run (this can take a while!)

9. When it's finished doing its magic, go to the Starnet folder, open up the _s version of your file and be amazed at the results!

Hope that's useful :thumbsup:
 

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I think that's a cracking M27 and I very much like the tenuous outer glow just as it is. The fact that you can get it to show more strongly doesn't mean that you have to. Yours feels very true to the object when I look at it. Given that the outer shell contains no fine details it can be stretched and noise reduced considerably harder than you have done here, I think, but it would be important only to add the shell and not the stars from any such hyperstretch.

Something I don't think anyone has mentioned on here is the Ps option to add noise. Why would you add noise?  Well, very occasionally I do. Anything extremely faint may need NR to the level of looking oily, which we all hate, but the judicious addition of a touch of noise can make it look natural again. Just doing less NR in the first place is not equivalent because it may be large scale blotchiness which the NR is killing and small scale noise which is added afterwards.

Olly

 

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Thank you Olly. I know what you mean about the NR / Noise equation! I particularly like your comment that this rendition '...feels very true to the object...' - that is completely my approach to astrophotography, so I am happy that perhaps I'm somewhere close to my goal!

However, inspired by Göran, I couldn't resist giving it a tweak. I'm not one for going mad, so I have just turned up the outer shell by a stop or so. I think I prefer it, but I'm now getting dangerously close to not being able to objectively assess the screen anymore - I've stared at this one too much now...

 

M27-BiColourRGB-06-Flat.thumb.png.db0a755fe3619396c579fab626d5e0f9.png

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Both are cracking images Gav, but I also do just prefer V2 with the stronger outer halo. I'm going to have to learn/experiment with Olly's equalize method.....

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Thanks Geof. I ended up using the Screen Mask Invert method that I know from I know not where, but it’s certainly not my invention! I gave Olly’s Equalise Method a go, but I need advice from the Master himself to understand how to make it work successfully. 

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1 hour ago, PhotoGav said:

Thank you Göran, I will have a go at teasing out more from the outer shell with the Equalize method. In fact, you make me think of the Screen Mask Invert technique that I forgot to try - I was so engrossed in the Starnet thing!

As for how to get the standalone Starnet version to work on the Mac, here's the method I used:

1. Download the latest version of Starnet for Mac OS from here: https://sourceforge.net/projects/starnet/files/v1.1/StarNet_MacOS.zip/download

2. Unzip the folder and place it on your Desktop

3. Save the image that you want to make starless as a 16 bit mono or RGB .tif file

4. Place the file in the Starnet folder on your desktop

5. Open Terminal and navigate to the Starnet folder (you can do this by pasting - cd ~/Desktop/StarNet_MacOS - into Terminal and hitting Enter)

6. Open in Text Editor either the file 'run_mono_starnet.sh' or 'run_rgb_starnet.sh' depending on whether you are working with a mono or RGB file and edit the filenames in there to be the filename of the file that you want to make starless

7. Drag either 'run_mono_starnet.sh' or 'run_rgb_starnet.sh' onto the Terminal window and you should see the path of the the file appear

8. Make sure that Terminal is the uppermost window and hit enter - Program will run (this can take a while!)

9. When it's finished doing its magic, go to the Starnet folder, open up the _s version of your file and be amazed at the results!

Hope that's useful :thumbsup:
 

Thanks a lot for that Gav - that is the type of instructions I needed! I will give it a try asap.

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Yes, that v. 2 is nice - I do not think it is overdone.

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7 minutes ago, gorann said:

Yes, that v. 2 is nice - I do not think it is overdone.

Good stuff. Thank you for pushing me to the reprocess. That’s what I love about this forum, there is such a wealth of experience and great suggestions. Good luck with the Starnet experiments - definitely worth pursuing.

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