A Glaring problem with the Jellyfish Nebula

[B4silio]

~17 hours in total of 180sec exposures on the Jellyfish Nebula:

• Hydrogen alpha : 5h20
• Oxygen III : 7h30
• Sulphur II : 4h

The Oxygen signal is really weak and I hoped to get something more by having more time on it but I don't know to what extent that helped.

My biggest issue is with the flare from the 2 big stars (Eta and Mu Geminorum), which is coming from the O3 and S2 Astronomik filters, I have no idea how (and if) I could reduce/remove it, or if it's simply one of the drawbacks of the filters?

I remain very jealous of the incredibly tiny stars I see in most images on this forum! 

Tak FS-60CB + ZWO ASI 1600M Pro + Astronomik Filters

[Davey-T]

Probably best to remove the stars, process the nebula then put the stars back.

Dave

[B4silio]

Thanks Dave!

Indeed it's what I've done for the smaller stars, my issue is with the largish stars, but even more, the huge lens flare around the 2 big ones, not really sure I can remove that 😭.

[SamAndrew]

Can you post the stacked files? I'll have a go and see what techniques can be used to get a better result with the stars.

[B4silio]

Hey Sam!

Thanks yes! Stacked channels should be attached here (hopefully).

In the meantime turns out a simple blurred round mask in photoshop got rid of most of the flare, so I think that settles it for that issue.

 

What remains is actually learning how to process stars properly (which remains something I'm very novice at). I'm happy to hear any advice on this. To give some context, right now my workflow is:

Pre-processing

1. Stack everything with APP, stretch image in PI
2. Use Starnet++ to remove stars, create a starless background and a stars only mask
3. Morphological erosion on the stars mask to reduce stars
4. Export both background and stars and switch to Photoshop (where I'm much more comfortable)

For the background:

1. Add all background layers, set blending mode for everything to screen and add a Colorize adjustment layer to each
2. Set S2 to Red, Ha to golden-green, O3 to green and O3 again to blue (this lets me play around to balance things)
3. Add curves to each of the layers and play around to adjust things
4. Merge all Background layers and use Camera Raw Filter to add some clarity, get rid of noise, etc

For the Stars:

1. Add Ha and O3 star masks and add a Colorize adjustment layer to each
2. Set Ha to orange-yellow, O3 to blue-cyan plus a saturation layer
3.  Put everything on a group with screen blending mode
4. Add a curves layer to bring luminance up a bit (the star masks tend to be a bit faded)

There is a bit of clean-up that I should be doing on the starless image, as it currently tends to have a lot of leftover glow from stars that were removed. And as all big stars remain in the "starless" image, they get stretched and blown with everything else.

Thanks for any tips and have a lovely evening!

JellyfishNebula-Halpha-18720.0s.fits JellyfishNebula-OIII-27180.0s.fits JellyfishNebula-SII-14040.0s.fits

[david_taurus83]

I have never seen halos or bloating like that before. What do the individual subs look like?

[B4silio]

The stars don't look that horrible in the individual stacks, I think it's in trying to push the O3 signal that the big splotches appear. As for the halos, it's likely the filters.

[B4silio]

getting the big stars out of the background and processing them separately improves things a lot, but I'm not really able to get rid of the flare underneath the big stars...

Edited March 20, 2020 by B4silio

[SamAndrew]

It doesn't look like you're using a flattener? I think that's the biggest problem causing the reflections to not be concentric as in the pic below:

The stars aren't even from corner to corner which would make me think collimation is off as well but that isn't as critical.

Apart from that, the 2nd attempt is decent! I can't do any better than that

[B4silio]

Hey Sam, thanks a lot for checking that out!

I'm using a refractor, so if collimation is off (which is quite possible!) that might be difficult to fix O_O. I am actually using a flattener, but it might be that my spacing is off.

Also stars are a lot more squished on the upper left corner, could that be due to the imaging train sagging down and making that screwed up?

What makes me pause is the fact that there's quite a bit of difference between filters, with Ha and S2 showing more microlens diffraction ("X" pattern) whereas O3 (center) has less of that and more rings.

There's clearly something weird going on with the scope/imaging train itself, but I'm far too inexperienced to understand where that could be coming from.

[B4silio]

Another pass off processing: I went back to the unstretched images to get the stars a little less burned out. I prefer this version (even if it does accentuate the flare-rings). I think that should more or less fix it in terms of stars, now the interesting challenge is how to avoid the ring holes in the background. (I suspect that making the entire background darker would already help quite a bit, but I tend to like better images that are not too black).

Thanks a lot to everyone for the tips and advice, if I look back at the top image, the change is quite something!

Edited March 21, 2020 by B4silio