Problematic Light P...
 
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2022-05-29: APP 2.0.0-beta2 has been released !

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Problematic Light Pollution Removal


(@andynowlen)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 52
Topic starter  

Hi,

In my images, I often am challenged by similar results of APP stack and light pollution removal attempts that show in the attachments.

For now this is my equipment:
Canon 5Diii astro modified
Canon 100-400mm f/4.5-5.6L ii
This image of NGC 7822 is at 390mm. 32x300second images.

I just wonder if there is a way in APP to avoid the three rings of brightness.  Dark at the borders, a lighter donut, then a darker center.  

Attachment 1 = Demo_v3a - Stretch to show the issue.  Stretch = 10%BG,3sigma,0,0% base, no light pollution removal.

Attachment 2 = Demo_v3b - Stretch to show the issue.  Stretch = 10%BG,3sigma,0,0% base, WITH light pollution removal attempt.

 

Demo v3b 10 3 0
Demo v3a 10 3 0

I appreciate any guidance.

Regards,

Andy


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(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 1719
 

Hi Andy,

Do you use flats with APP? If yes, how do you take them? To me it looks like an issue where the flats overcompensate the lights. This is not light pollution.

 

Wouter


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(@andynowlen)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 52
Topic starter  

@wvreeven

Thank you. I expect you are correct. I did use flats shot with a light panel.  As I am learning AP I think my flats exposure time is too short.  

On the journey.....

 

Andy


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(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 1719
 

@andynowlen

As a rule the peak of the histogram of the flats should be between 30% and 70%. If your exposure time is too short then the peak will lie to the left of that and you indeed should increase the exposure time.

Wouter


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4830
 

And it probably also depends a bit on how short your exposure was. If it's like 1/1000 of a second, it may also be that the sensor data is not behaving properly. This also is an issue sometimes with bias, take bias at at least 0.05 seconds and flats at around a second(or higher than 0.05) at least. Also make sure that you need to calibrate your flats with bias or darkflats and just once, not twice by accident.


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(@snowman)
Molecular Cloud Customer
Joined: 2 years ago
Posts: 5
 

In cases where there is nebulosity everywhere and no obvious areas of dark sky background how do decide where to place the squares?. I am new to APP but have had success with your example of the large magellanic cloud but I downloaded some data to practice on which seemed to be all nebulosity and am at a loss as how to proceed.

Mike Evans


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4830
 

Sorry to have missed your question, in cases like that there aren't many options. I would stretch to the max (30% setting) and up saturation. Then I'd select a few regions where the nebulosity is lowest and see if that works for the overall image.


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(@snowman)
Molecular Cloud Customer
Joined: 2 years ago
Posts: 5
 

Thanks, I'll try that

Mike


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