Orion - belt to sword - 4 panels HOO mosaic

[alexbb]

Hello all,

I'm starting a new thread for this since the hydrogen data is rather old and it has been reprocessed since I posted a while ago.

Now I finished the acquisition of O[III] too. Or sort of, I planned more, but clear nights were so rare that I decided to process what I had.

The image was done in "3 pass" data over the area. That means that I acquired 3 sets of images covering the same area and combined in the end. First 2 in hydrogen, the last in oxygen.

First set consisted of 3 panels in portrait mode for the top area and then I wanted to extend them to the bottom so I shot another 2 panels in landscape mode.
I knew that I could get a higher SNR so I shot 4 more panels in landscape mode.
Each panel consists of 30-31 subs, each sub 300s.

Then I started the acquisition of O[III] which needed light pollution and moonlight conditions than the Ha required.
Top panels contain 30 subs, but the bottom ones, only 20-22. Each 300s. Luckily there's not much oxygen in that area so I could get away with less subs.

I also took some 10s-30s frames for M42's core.

For the framing, I created a quick mosaic of the same area.

For the final alignment I shot an image somewhere close to the center of this area. I can't remember if the initial register was done in APP or Registar - for the first pass, but for the next ones it was done in Registar.

I removed the gradient manually in each stack with APP and then I created the mosaics for each pass same with APP.
The 2 Ha passes I then blended manually 50%-50%.

For the processing, I tried to stretch both Ha and O[III] to the same levels and I combined them manually in some 60-40/70-30 ratio for a layer which I used as lum.
The colours were Ha - reddish, O[III] - cyan-blue.

I spent a lot of time trying to control the big stars, the O[III] filter has poor coatings and, together with the ASI1600s non AR coated sensor, I had much brighter reflections than with the Ha filter.

And I tried to raise the oxygen levels selectively around the flame and NGC2023, but the flame is really dim in O[III].

Don't know what other details in the story I forgot, this project drained me a lot of energy.

Camera was ASI1600MMC, cooled to -15C for the first pass and to -25C for the ones following. Gain 139.
Canon 300 F4 L IS lens with a lot of aberrations towards the edges.
AZ-EQ5 mount guided with a 200mm lens and an ASI120MM, with varying seeing. 1.5-2.5" RMS guiding error usually.

APT for capture, PHD2 for guiding, Registar for each night initial alignment.
DSS, APP, Registar, StarTools, GIMP for processing.

I started shooting early in October and I wanted much more, but Orion already becomes less and less visible from where I image and hides beyond the house. Ah, yes, I image from a yellow-pink light polluted area.

Thanks for reading, thanks for looking! Comments and suggestions are appreciated.

Links to original image and acquisition details:
https://drive.google.com/open?id=17tr8lqagQAJg8maojtHZPbM-f67gSBTv
https://drive.google.com/open?id=12gjGEgeR7FxR1Tow0e64JczeeUIqKojK
https://www.astrobin.com/330284/

Alex

[Randalloverby]

Wow, very nice.

[Whistlin Bob]

This really is a "Wow" image. Thanks for sharing not only the image itself but also, in detail, the steps taken to achieve it. I hope that this result gives you the sense of satisfaction that your efforts deserve.

[alexbb]

Thank you, guys!

I added a new less red version. Which one do you prefer?

[Scott]

Stunner!

 

[M Astronomy]

Awesome images. I personally prefer the second one.

 

[MikeODay]

Fantasitic image.  I did not know the dust and gas clouds were so extensive.  Thanks for sharing.

[alexbb]

Thank you all!

I just saw the last version on the tablet and I noticed that in the top-right panel the stars were mostly blue. Now fixed. I think this is due to APP trying to bring the backgrounds of all panels to the same level, but being shot over multiple nights, I don't expect the same value.

[Whistlin Bob]

5 hours ago, moise212 said:

Thank you, guys!

I added a new less red version. Which one do you prefer?

For my part, I personally prefer the second, less red, version. Main reason is just that the colours look (a little) closer to what you see as a visual observer.  Both are beautiful images.

[alexbb]

10 hours ago, Whistlin Bob said:

For my part, I personally prefer the second, less red, version. Main reason is just that the colours look (a little) closer to what you see as a visual observer.  Both are beautiful images.

Thanks, Bob!

Yeah, close to what you see visually..
It's been more than a year since I haven't seen through an eyepiece the M42 from a dark site. I recall it had a green-ish tint around the core.