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Struggling to get good results on images with high nebulosity  

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(@ashleypowell)
Molecular Cloud Customer
Joined: 1 year ago
Posts: 3
August 18, 2021 02:30  

Hi guys,

 

My first post here after using APP for a while now.
Generally I find it really great and get good results however I really struggle with images that have a lot of nebulosity and seem to get poor results.

For example, I am currently trying to process M16 and am really not pleased with the results. The colors seem way off and I seem to lose a ton of nebulosity via use of the various tools. (Light pollution removal and star color calibration)

These issues are common whenever i process this type of object.

My equipment;

- ASI533MC Pro camera

- William Optics Z81 with 0.8x reducer/flattener

My workflow is generally;

- Manually set bayer pattern and force bayer CFA option.

- Use lights, flats, dark flats and darks

- Skip straight to "integrate" and use all defaults/automatic settings.

- Use Crop, Light Pollution and Star calibration tools, occasionally HSL color and most recently the star reduction. (the latter is great!)

The data below consists of;

- 54 x 600s lights over two sessions. (OSC RGB)

- 100 flats (50 per session)

- 100 dark flats (matching above)

- 20 darks.

Ive attached the progression of images below from crop only, through light pollution, star calibration and star reduction.

I can also upload the raw fits if needed.

Thanks!
Ash

 

 

M16 Stretch settings
M16 LP CSC StarReduce
M16 LP CSC
M16 Light Pollution
M16 Crop only

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(@astrogee)
Neutron Star Customer
Joined: 3 years ago
Posts: 127
August 18, 2021 13:34  

I have the same work flow. It seems the problem is at star calibration. I often wondered how the nebulosity affects the star colour. I imagine that if the star is in the foreground, then its not a problem but if the star is in the background then its light is filtered through the nebulosity itself and calibration with throw off the colour. So I always try to place the calibration boxes in the areas with no nebulosity, which is difficult of course with lots of nebulosity - similar to background and light pollution tools, you have to avoid the nebulosity when making selection boxes - Check out Mabula's tutorial on using the light pollution tool - he slowly works through the frame making small boxes in selected areas, looking for background only.

This post was modified 2 months ago by astrogee

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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3861
August 19, 2021 19:06  

Usually I stretch the image to the max, to be able to see nebulosity better. Then I do the light pollution correction on the area's where there is no or very little nebulosity. If not, you may reduce nebulosity indeed.

Regarding color correction, this usually works very well, but if you use narrow-band data, which is not broadband, it's not of great use. This is because it uses black body radiation from stars to determine the color and these need to be broadband as a signal to work well.


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(@ashleypowell)
Molecular Cloud Customer
Joined: 1 year ago
Posts: 3
September 18, 2021 10:46  

@vincent-mod
Thanks and sorry for the slow reply.
Yes I use the same method, I use the 30% stretch, full saturation, no saturation protection etc.

Im fairly frustrated at this point. Take this example of the veil, no matter how many or how few, or how well placed the selection areas, I just have this ugly residual "haze".
Id really be interested in seeing what you could do with my data, if you have time or inclination. Maybe im battling some issue deeper than the light pollution tool?

https://1drv.ms/u/s!AgHakjPeM-lyzj3VLzNVuapAxugQ?e=TkWsu9

Veil LRP

 


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(@gary-clayton)
Brown Dwarf Customer
Joined: 1 year ago
Posts: 8
September 18, 2021 11:07  

@ashleypowell

Hi Ashley, I just ran your data though APP and it came out ok, your signal to noise ratio is high though did you use a light pollution?

NGC6960 session 1 session 2 session 3 session 4 session 5 crop  90degCW 1.0x LZ3 NS St

filter?


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(@ashleypowell)
Molecular Cloud Customer
Joined: 1 year ago
Posts: 3
September 18, 2021 11:10  
Posted by: @gary-clayton

@ashleypowell

Hi Ashley, I just ran your data though APP and it came out ok, your signal to noise ratio is high though did you use a light pollution?

NGC6960 session 1 session 2 session 3 session 4 session 5 crop  90degCW 1.0x LZ3 NS St

filter?

Thanks, Gary. It certainly looks 100% on what im achieving....

No I didnt, im in Bortle 4 and it was new moon. That said, the object was quite low in the sky and there is definitely glow on what was the low side.
I think theres about 14hrs in that though, which I had hoped would be adequate..


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(@gary-clayton)
Brown Dwarf Customer
Joined: 1 year ago
Posts: 8
September 18, 2021 11:45  

@ashleypowell

I am also imaging in bortle 4 and have the same setup as yourself, as far as processing your data I used 6 very small boxes in the light pollution section of APP which seemed to do the trick. The image below is 32x5 mins with the an Optolong L-eXtreme filter as it makes a big difference with this camera.

Veil nebula
Veil nebula

 

This post was modified 1 month ago by Gary Clayton

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