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RCC (Request for Constructive Critique) on the Horsehead Nebula

Pleiades Astrophoto PixInsight SHO LRGB Monochrome Request for feedback
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Tommy Mastro avatar
Tommy Mastro avatar
Hi.  This is my first post in this forum and my second attempt at processing a Mono image (I received my first mono camera a few days ago).  I took the image below using SHO and LRGB filters (see acquisition details for integration times and such).

I processed using Pixinsight.  I use the new technique Cuiv discusses where you convert your raw stacks to RGB format and color them before you combine.  HA Yellow/Gold; SII Red/Yellow; and OIII Blue.  Obviously my RGB also gets assigned accordingly.  Then I combine in PixelMath.  I also perform noise reduction, then stretch, before combining.

Once combined I use SCNR to remove any excessive green, then Invert Image and use SCNR green removal again (inverted) to remove the excess magenta.  Then tweak color, saturation, and curves.  Then unclarity and a final noise reduction if needed.

Oh, most importantly, I removed the stars from SHO before combining but left the RGB stars in for combining.  When I had a consolidated image, I removed the stars to make the tweaks mentioned above, made some tweaks to the stars (mostly saturation and BXT), then used PixelMath to put the stars back.  

Please, all criticism is welcome.  I am still a raw NOOB when it comes to mono processing.

Horsehead Nebula 2024 (SHO and RGB) (tom62e) - Full resolution | AstroBin
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Tony Gondola avatar
Tony Gondola avatar
I like the color and detail but the stars look odd to me. The added diffraction spikes are just really over done. If this was shot with a Newtonian you wouldn't see bright spikes on the fainter stars in the image.
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Tommy Mastro avatar
Tommy Mastro avatar
Ha!  I debated that for a while.  When I work up this morning and looked at it with fresh eyes, I thought the same thing.  

In the past I tried using a 3D printed diffraction spike mask in the front of the corrector plate, but it made super-long spikes that I didn't like, so I tried the software route.

Thanks for the feedback!
Tony Gondola avatar
Tony Gondola avatar
Haha, great minds!
Charles Hagen avatar
Charles Hagen avatar
There are a couple major items I see here. Of course as has already been noted, the software diffraction spikes are rather distracting. Aside from that, there is a double "shadow" of the horsehead, presumably from a misaligned layer / mask as seen in the attached image. The colors in general seem off as well. The blue near the bottom left appears to be an uncorrected gradient rather than any cosmic structure. The noise reduction feels overdone as well, the nebulosity in the background is very soft, much of the fine detail that I believe is likely present in the original data has been lost. As just a matter of personal preference, I would rather see that detail paired with a bit of natural noise, rather than the plasticky appearance that you'd get with excessive noise reduction.

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Tommy Mastro avatar
Tommy Mastro avatar
Agreed about the NR.  I saw that this morning with fresh eyes as well.

Regarding the blue gradient, you must be a master.  When I ran the gradient removal, it took away 90% of the blue.  I mistakenly assumed the blue was part of the image and needed to be there, so I used "undo" to replace the blue and moved forward without the gradient correction.  This might also explain why the blue was so much noisier than the rest of the image (which is one of the reasons I cranked up the NR).

I was wondering about the double horsehead "shadow".  I went and looked at other HH nebs and couldn't find another one with such a shadow.  It's weird that the stars would have aligned but not the HH.  Ahh, wait, I think I know what happened.  When I combined the NB and the LRGB, only the LRGB had stars, hence there would be no alignment issue with the stars and only with the nebula.  I bet if I compare this to another image, the stars are probably slightly out of place.  

Still, why would there be an alignment issue at all?  It must have happened when I added the LRGB filters to the FW.  I took the front half off the optical train off (took it apart at the Celestron OAG) so I could add the newly purchased LRGB to the FW.  I presumably replaced it in the exact same orientation as it was, but perhaps I inadvertently changed the spacing.

Lots of lessons learned today!

Thank you.
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