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Help! Ugly gradient lines after stacking multiple nights in DSS

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#1 hdoraisamy

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Posted 02 August 2021 - 04:39 AM

Hi

 

I was attempting to image the veil nebula with my Canon EOS Rebel T6 (modified) with a 200mm Pentax prime lens on a Skyguider Pro with iPolar. I got good polar alignment and captured approximately 24 min of light subs for the 1st night and 30 min of subs for the second night.

 

When I tried stacking them in DSS, I put the 2 nights in separate "groups". I used the same darks, bias and flats from night 1. The temperature was not much different.

 

However, as you can see, DSS ends up creating an ugly gradient below

 

problem
 
I looked at my subs in more detail. The subs in night#1 have a different reddish tinge than the subs in night #2 as you can see below
 
reel1
reel2

 

I tried using different stacking techniques - Standards, Mosaic, Intersection, but no joy! I think the color difference between the 2 nights messed me up. Same results with Sequatror.

 

I do not know why this exists? Light pollution? The moon was not out either of these nights

 

How can I correct this? Is there is specific workflow? I only have DSS, Lightroom and Photoshop.

 

For the record, both sets give me a nice image of the veil complex, but i want the combined stacked image to reduce the noise.

 

Appreciate your guidance! Thank you so much!

 



#2 michael8554

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Posted 02 August 2021 - 06:24 AM

Do you mean the area I have bordered with the white lines ?

 

2ndJuly.jpg

 

This is because your camera was at different angles of rotation on the two sessions.

 

In DSS you can select a number of final framings.

 

If you select Intersection mode you will get the area where the two night's images are matched.

 

2ndJulyB.jpg



#3 adosaj

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Posted 02 August 2021 - 06:57 AM

I use APP for data reduction and there is a parameter when you are integrating all the subs into one that basically sets the background value by looking at the local neighboring pixels. There must be a similar parameter in DSS. It blends the two nights’ backgrounds evenly. 
 

Anil


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#4 hdoraisamy

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Posted 02 August 2021 - 07:40 AM

Do you mean the area I have bordered with the white lines ?

 

 

If you select Intersection mode you will get the area where the two night's images are matched.

 

 

That is correct - I tried intersection as you suggested. It fixed the problem with the color gradient :) But it made the stars bloated and less focused. I also have weird issues around the corners. If I stacked each night separately, they came out very well. 

 

See result of stacking by intersection (with darks, flats and bias)

 

bloated stars



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