Pacman Nebula IC11/IC1590/LBN616/LBN123.17-06.28/NGC281/Sh2-184 (c-sho)

[ramdom]

Also includes: Multiple star B 1, Bok globules.

Total integration: 16 hours/960 minutes = 54x5m for S2 + 90x5m for Ha + 48x5m for O3.

Camera: QHY163M (16mp mono) CMOS cooled to -15 degrees C.

Telescope: Takahashi FC100DF Steinheil fluorite doublet apochromat refractor @ f/7.4.

Reducer: None.

Mount: Paramount MyT.

Filters: Astrodon 5nm Ha, 3nm O3, 3nm S2.

Software: Sharpcap, PixInsight.

More detail and different versions with full resolution are here:  https://www.astrobin.com/h9xku6/ -  I uploaded reduced sized images  to show you the starless version (C) also; the corresonding image with stars is (B) at AstroBin. 

The Pacman Nebula (IC11/NGC281/Sh2-184) is a bright emission nebula part of Cassiopeia about 9200 light years from us. The nebula derives its name from the video game and in this case, the nebulosity is spans a diametre of 92 light years (so perhaps bigger than its name suggests but very small in the context of the rest of the universe).  It contains several dark nebulae within it known as Bok globules, a multiple star in the middle (B 1 or beta 1, which is a quintuple system), as well as the open cluster IC1590.

This, like the Wizard Nebula, a popular target for narrowband astrophotographers.  The only difference between this image and the last one I did of the Wizard using this almost exact setup (FC100DF at f/7.4) is a Starlight Instruments microfoccuser (MPA-TAK2.5) I installed which let me fine tune the focus which wasn't possible with the factory origin Tak.  I had been using the coarse focus which was tolerable at f/4.9 but at its native focal length you can see the difference in the detail and the lack of fuzziness (I'm quite positive my seeing was about the same; average). The double star in the middle of the nebula, and part of the quintuple system, is partly resolvable as two half-spheres.

I finally had some success applying a starless technique in PixInsight and I've included versions of the nebula without stars (C) and also an image processed without stars and then the stars added back (B). An additional colour choice is (D) since I find the SCNR palette to be repetitive at times, and as always the Ha only image is (E):

https://www.astrobin.com/h9xku6/C/

https://www.astrobin.com/h9xku6/B/

https://www.astrobin.com/h9xku6/D/

https://www.astrobin.com/h9xku6/E/

I think both the main image (A) and the reconstituted starless image (B) look pretty good, with subtle differences that I think will come down to preference. There's some colour noise I was able to tame with TGVDenoise but I've yet to figure out how to sharpen the details while avoiding noise entirely (deconvolution is the next thing I need to learn). Until then, the minimally processed Ha image is where you can see the minute details the most.

As always, thanks for looking!

--Ram

[x6gas]

If you are looking at deconvolution in PI then I thoroughly recommend Jon Rista's tutorial.  Be aware, though, that deconvolution will tidy up the data a little but won't do much to sharpen detail in the nebula.

[ramdom]

Thanks! It looks helpful - I have been following the LVA tutorial except for using the PSFImage script to generate the PSF (I did it manually once and this script seems to do better) from Herbert Walker's page (it's a great tool if you've not used it before). And yes, it does exactly as you say - cleans up the data but not sharpen exactly.   

This is a bit tangential, I've been playing with this great dataset (60+ hours worth) of sh2-132 (Lion) that is frustrating to me and I've thrown everything I can at it but the best SHO image I can generate looks okay but not great but I am able to get HOO images to look near terrific and I know this dataset is great because someone else was able to work magic with it (via HOO again).  This is Stephen King's HOO version: http://ram.org/images/space/downloads/sh2-132_sho.v0.1.jpg and this is my solid B quality image (I'm working on the A quality image now) of the SHO/HP:  http://ram.org/images/space/downloads/sh2-132_sho.v0.1.jpg

There are two major problems: this target has a vast amount of stars in the background  and the SHO introduces colours in a way that ruins the detail (I've seen this happen so often - this is why I post Ha images on my AB page for all targets - the monochrome images can perceptually capture detail that colour images seem to mask). 

If anyone is really interested in playing with the dataset, the XISF files are here: http://ram.org/images/space/downloads/sh2-132_Ha.v1.2.xisf (substitute O3 and S2 for "Ha" and you'll get the other two). The only thing done to it is DC and DBE, no other processing. If you want the files without that, if you substitute "v1" instead of "v1.2" you'll get the original master lights.

--Ram

PS: Also the starless image looks terrific: http://ram.org/images/space/downloads/sh2-132_sho.v0_starless.jpg  - so again I know the data is there - I just want the nebula to show like that but with the starry background.  A simple morphological transformation (default erosion) illustrates my point (or if I go to Nebulosity and hit "Sharpen" and to 2.0) and I normally don't like to get rid of all the tiny stars but this case may be an exception.  

[Datalord]

4 hours ago, x6gas said:

but won't do much to sharpen detail in the nebula.

I think I'll have to disagree with this one. Decon is a seriously good tool to sharpen nebulosity. So much so that I sometimes go a little too far with it, but it definitely works on nebulosity.

31 minutes ago, ramdom said:

this target has a vast amount of stars in the background

I have the same problem on all nebulae. They're obviously in the Milky Way and both the RC and RASA are photon buckets. Any substantial amount of integration time will have the image lighting up like a Christmas tree. I just reduce their size, but I very rarely go full starless. All those stars tell their own story.

 

On 10/07/2020 at 21:33, ramdom said:

Takahashi FC100DF Steinheil fluorite doublet apochromat refractor @ f/7.4

I can't help notice you have some pretty serious vignetting in many of your images. How do you calibrate the images?

[ramdom]

18 minutes ago, Datalord said:

I have the same problem on all nebulae. They're obviously in the Milky Way and both the RC and RASA are photon buckets. Any substantial amount of integration time will have the image lighting up like a Christmas tree. I just reduce their size, but I very rarely go full starless. All those stars tell their own story.

Yeah, when I do the starless thing,  I  put the stars back at a reduced size for this target (which for the smallest stars makes it disappear) but normally I prefer not to do this - each star as you say has its place. 

As far vignetting, are you referring to the OSC images with the 247C? If so, then I use flats and I have this routine involving flats and flat darks which I subtract to create a master flat dark and it works great for the dust bunnies and such but really seems to be introducing more gradients than not especially once I do the DBE.   So I just live with it. Plus I rarely invest time into OSC images - I bought the camera as a way to get to targets like galaxies and reflection nebulae without too much effort and plan to go  back someday with a proper RGB setup.

With the NB images (163M), it's a hit or miss situation depending on whether I see any dust bunnies but I definitely don't see vignetting in any of them.  If there is any darkening towards the corner due to the light drop off due to the cosine gradient, it is again because I've not gotten flats calibration to work properly - I definitely can and do take them with regularity (I keep my camera and scope mounted together for usually a whole season but definitely several weeks at a time) but they don't seem to help with the cosine gradient.  

--Ram

[ramdom]

And if you're referring to the right hand corner that is very dark above, that's due to me (poor) masking out the amp glow which is terrible, see the bottom part of this for instance: http://ram.org/images/space/scope/1.4.4.5/veil_sho_20+10x360s_61+20x360s_34+15x360s.jpg

---Ram

[Datalord]

Hmm, might be amp glow. but yeah, the lower right hand corner always seem to light up.

[ramdom]

Yes, definitely the amp glow, or an internal light leak. So in the Pacman image I obviously overcorrected  but in others  I've been able to mask it out or tame it. In my oldest images I struggled with this problem for a while also but I finally got a handle on it enough so that a decent mask plus proper calibration does get it like 90%. The amp glow is actually all along the right, both top and bottom with the middle taking a break. But now I've gotten it so it's only in a small portion of the bottom right corner after calibration. Another issue I struggled with the first year or two...  (this is year 3).    

--Ram

 

[x6gas]

2 hours ago, Datalord said:

I think I'll have to disagree with this one. Decon is a seriously good tool to sharpen nebulosity. So much so that I sometimes go a little too far with it, but it definitely works on nebulosity.

Well fair enough - though I didn't say its doesn't work on nebulosity - just that it won't do much to sharpen it... which has been my experience.  Be interested to know if you use different settings on stars and for the nebula.

[x6gas]

3 hours ago, ramdom said:

Thanks! It looks helpful - I have been following the LVA tutorial except for using the PSFImage script to generate the PSF (I did it manually once and this script seems to do better) from Herbert Walker's page (it's a great tool if you've not used it before).

Yes +1 for PSFImage.  Like you I've done it manually and PSFImage seems at least as good and 100x quicker.