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Bubble Nebula with STC-DUO

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Neutron Star
Joined: 6 years ago
Posts: 55
Topic starter  

I have been unable to image for months now (Netherlands), so have done some work on data acquired in the fall.


Imaging Location: My backyard (orange zone)

Telescope: Ritchey-Cassegrain  (prime focus). F=1000mm F/D=3.0

Camera: QHY168C

Filter: STC DUO dual narrowband filter

The picture above is 1 hour of acquisition in RGB (for the stars alone) and 6 hours with the STC-DUO (taken with and without moon in the sky, up and until about first/last quarter). 

Processing was not so straightforward. It is my first narrowband image and a lot to learn still. But it is nice that APP can separate HA and OIII as it gives more freedom than a regular AAD integration:

In APP it is relatively easy: Extracting a HA image from the data, Extracting a OIII image from the data, integrating the RGB image, register and combine in APP.

Here are the original results







As you can see, there certainly is OIII in this nebula.

I had a difficult time getting OIII to show up. It is easy to end with a red-only nebula. After looking at what others did, I used the combined result from APP (mostly red) as my base layer. I removed the stars from the (mono) OIII and HA images (slow and difficult process), increased the contrast of the nebulosity. I made a red HA image, a blue OIII image and a green OIII image and played and experimented in Photoshop with the ratios to get OIII to influence the color where there is OIII data (from red to pink/magenta..this is arbitrary, but I looked at the RGB image for inspiration).  After that I used the original RGB image as the top layer to preserve the star colors (using a star mask). 

It took a long time to get this and I am still not sure that I found a workflow that is repeatable and efficient, but looking at Astrobin for other images of the same region, I think the result is not too far off.


This topic was modified 5 years ago 12 times by Annehouw
This topic was modified 5 years ago 2 times by Mabula-Admin

Universe Admin
Joined: 6 years ago
Posts: 3815

Great result Anne @annehouw,

And thank you for sharing your workflow and results with the STC-DUO filter.

Did you try to process a composite in APP with the RGB Combine tool? Or did you only try Photoshop for the composite?

There definitely is OIII there 😉

Kind regards,


Neutron Star
Joined: 6 years ago
Posts: 55
Topic starter  

Thanks, Mabula

"Did you try to process a composite in APP with the RGB Combine tool?"

Yes, I did and it works great!

Below is my first effort. You can see OIII near the bubble (and the blue halo around the brightest star....), but it is not very obvious and still too monochrome.

NGC7635 combine RGB image SC St 1

Then I played around a bit with other ratios and got the image below. This image goes from deep red via yellow to purple (ish) near the bubble. Much nicer color separation than my first try. Never mind the ugly star cores, that is me being too enthousiastic with the HL slider. User error.  

NGC7635 combine RGB image SC St 2

I like the colors in this image a lot because it gives some extra depth to the image in my opinion.

The stars are giving me trouble though. There is quite some haloing going on, especially in the blue channel. And the stars are mostly white (due to the STC DUO filter). So, I decided to replace the stars alltogether with the stars from the RGB image I took as well (and registered to the OIII an HA images). I could have used this HA/OIII image to do this, but I decided to do it in another way: Remove all the stars from the mono HA and mono OIII images (a lot of work!). Then process these images do noise reduction and (a lot of) contrast enhancement and paste the RGB stars back in. The advantage of this is that you can do a lot of work on the nebula without increasing star bloat. This took me to photoshop, so I did the color combine there. I also performed halo repair on some stars and general star size reduction. 

The pushed starless HA image is below. I did tone these components down a in the final color composit, since it can get too heavy handed very fast and you start to see artifacts. So I ended up with using mono HA and OIII layers (HOO for RGB) and use these starless images to increase the contrast a bit for the HA and OIII layers before adding the RGB stars back in. 

NGC7635 36360s Ha lineair withoutStars


This was a long "yes"  🙂 

This post was modified 5 years ago 7 times by Annehouw

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