Cave Nebula (Sharpless 2-155) in HaRGB...

[Hallingskies]

As it was clear last Saturday I decided to grab 10 x 250s RGB subs (2x2 binned) to add to the mono data I already had for this one, despite a gibbous waxing moon.  The data wasn't great but I don't think it scrubbed up too bad in the end...

I don't use Pixinsight or Adobe, so over the years I have worked out my own way of doing things in the much simpler PaintShop/Astroart combination.  In the extremely unlikely event that anyone is interested in how I combine Ha and RGB data in such deeply unfashionable and old-fashioned software,  my blog post explains all.

[Rodd]

Nice detail in the "horn" region of the toad (not sure why its called the cave nebula when it looks like a lungfish crawling across a mud flat).  The amazing aspect of this image is the fact that broadband data was collected during a bright Moon!   Slight ringing around the smaller stars in the brighter areas. But I think it looks pretty good.  I think the Ha insertion has robbed you of star color.  Do you protect the stars during the insert?  Unfortunately (when adding Ha), this target has a faint but conspicuous reflection nebula that gets eliminated when Ha is added.  It may be possible to protect the reflection nebula during the Ha insertion and preserve it.  Not sure how you protect features in the software you use.  In PI its masks, in PS its layers.  Nice work

Rodd

[Hallingskies]

1 hour ago, Rodd said:

Nice detail in the "horn" region of the toad (not sure why its called the cave nebula when it looks like a lungfish crawling across a mud flat).  The amazing aspect of this image is the fact that broadband data was collected during a bright Moon!   Slight ringing around the smaller stars in the brighter areas. But I think it looks pretty good.  I think the Ha insertion has robbed you of star color.  Do you protect the stars during the insert?  Unfortunately (when adding Ha), this target has a faint but conspicuous reflection nebula that gets eliminated when Ha is added.  It may be possible to protect the reflection nebula during the Ha insertion and preserve it.  Not sure how you protect features in the software you use.  In PI its masks, in PS its layers.  Nice work

Rodd

I was a bit clumsy on the selective mild sharpening around the mouth of the cave, and you are right, there is some ringing there.  That’s easily fixed.  Combined the blend in “lighten” mode should let the star colours through and compared to the RGB it seems to have mostly been successful.  I could try a star mask to see if that is any better, so thanks for the idea.  In terms of the reflection nebulosity, my RGB data didn’t go deep enough to pick it up.  I did try H-beta, but there was none detected using the Ha exposure conditions, and it was too moonbright for Olll.   Maybe adding some deep Olll to the mix would help find some blue stuff somewhere when it gets a bit darker.  I’m under Bortle 4-5 and the B in RGB often seems to suffer.  Thanks for the suggestions.

[Rodd]

5 minutes ago, Hallingskies said:

 I’m under Bortle 4-5 and the B in RGB often seems to suffer.  

This may explain why I have trouble at times with blue....never thought of that.  Thanks!

Rodd

[Hallingskies]

Just now, Rodd said:

This may explain why I have trouble at times with blue....never thought of that.  Thanks!

Rodd

Blue data seems much crisper when gathered from a dark site, the difference isn’t so noticeable at other wavelengths, at least not in my experience.  But I have gotten too old and too lazy to lug my kit about these days...

[Rodd]

5 minutes ago, Hallingskies said:

Blue data seems much crisper when gathered from a dark site, the difference isn’t so noticeable at other wavelengths, at least not in my experience.  But I have gotten too old and too lazy to lug my kit about these days...

I do know that the blue filter should be employed when the target is highest--near the meridian.  I try to do this, but can't always due to having sporadic imaging sessions on account of the weather

Rodd

[Hallingskies]

7 hours ago, Rodd said:

This may explain why I have trouble at times with blue....never thought of that.  Thanks!

Rodd

Rodd; following your suggestions I masked the background in the RGB stack and then cranked up the saturation in the stars to try and improve the depth of colour before blending with the Ha channel.  I think it has brought out some of the blue stuff that was lurking in the data.  I also left out the sharpening of the cave region that was causing the star ringing in that area.  Has it all worked?  Maybe....

Another reason I think I struggle with blue stuff is that my old and beloved Vixen refractor is an achro, not an apo. Broadband blue is always a bit mushy as a result, though it is much better in narrowband. You can see the halos around the brighter blue stars, though I quite like that effect...

[Rodd]

1 hour ago, Hallingskies said:

Has it all worked?  

Absolutely--a definite improvement.  Nice cave. If you ever want to get rid of the magenta halos--invert the image and see if the halos are greenish.  If they are, and there is no other green in the image, SCNR green will eliminate them ( actually any color that is not elsewhere in the image.  Inverted colors are opposite.  If the inverted halo color IS in the image elsewhere, create a loosely fitting star mask and apply it to the image after you invert it, then use SCNR red/green or blue and they will be gone.

Rodd

[Hallingskies]

9 hours ago, Rodd said:

....SCNR green will eliminate them ( actually any color that is not elsewhere in the image.  Inverted colors are opposite.  If the inverted halo color IS in the image elsewhere, create a loosely fitting star mask and apply it to the image after you invert it, then use SCNR red/green or blue and they will be gone.

Rodd

Forgive my ignorance - what’s SCNR?  But if it works for fixing magenta haloes then you’ll have my thanks.

[Rodd]

4 hours ago, Hallingskies said:

what’s SCNR?

It is a Pixinsight tool.  I think it is classified as noise control, though the primary visual effect is to remove excess saturation.  Green is the most common use--but for the removal of colored star rims or halos it is useful for all colors.  If you use PI--just look for SCNR and it is pretty easy.  If not, that explains the reverberating echo I hear as I shout into the void!

Rodd

[Hallingskies]

Ah, PixInsight.  I don’t do that.  Yet.  I may well invest in the time and effort Pl will take, once I can consistently get good enough data to feed into it.