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What is wrong with my flats ?


(@jarbi58)
Main Sequence Star Customer
Joined: 5 years ago
Posts: 34
Topic starter  

Hi,

Recently I have tested my Canon 6da fullframe DLSR on a TS 150mm F/2.8 Hyperstar scope, and I took the usual calibration frames. For better understanding, I have shared these together with one light frame here: https://drive.google.com/open?id=1N1P6j8AFUX3W7WPxWGnTfMwjMe3sBOH7

It looks like applying flats has almost no effect on the vignetting in the final image, it looks like this:

M51 stacked

When I try to use the light pollution removal tool, it gets even worse:

M51 light pollution removal

Could you please shed a light what am I doing wrong here ? As far as I see I followed the usual guidelines to make the calibration frames,

 

Clear skies,

Janos


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4736
 

This could be light pollution which isn't coming from a sky gradient. So that would potentially be, internal reflections caused by a light somewhere near.. it's hard to pinpoint.


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(@jarbi58)
Main Sequence Star Customer
Joined: 5 years ago
Posts: 34
Topic starter  

Thanks Vincent, that is very plausible under my Bortle 7 skies... I think I will stay at narrowband imaging, then I have hopefully no such effect,

 

CS,

Janos


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4736
 

That might be the cause indeed, are there any lights shining directly into the direction of your setup? Even from rather far away?


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(@jarbi58)
Main Sequence Star Customer
Joined: 5 years ago
Posts: 34
Topic starter  

I don't have lights nearby the setup and I have a 25 cm long dew shield in front of the telescope, that prevents normally any stray light. What I suspect is that the sky background is too bright, even with light pollution filter. My scope is a TS 150mm f/2.8 Hypergraph, so very quick for these circumstances.

 

 


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4736
 

Oehh right, those kind of setups are indeed very sensitive for light reflections. Still I would say this looks like there is some kind of internal reflection going on, maybe it's a good idea to double-check the setup for specifically this? Could also be that internal parts are a bit too reflective.


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(@chrispeace)
Main Sequence Star Customer
Joined: 4 years ago
Posts: 43
 

I know this is an old thread but I recently tried taking Flats with a SW 150PDS in my darkened garage and had weird light patches in my flats. Seems the back end (mirror end) of my scope and I suspect any reflector, leaks stray light like a sieve and you don't need much.  So now I either do flats at night in the garage or wrap both ends of the scope in a blackout material or similar. I saw an immediate loss of stray light artifacts ensured. 

Chris

This post was modified 2 years ago by ChrisPeace

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(@jarbi58)
Main Sequence Star Customer
Joined: 5 years ago
Posts: 34
Topic starter  
Posted by: @chrispeace

I know this is an old thread but I recently tried taking Flats with a SW 150PDS in my darkened garage and had weird light patches in my flats. Seems the back end (mirror end) of my scope and I suspect any reflector, leaks stray light like a sieve and you don't need much.  So now I either do flats at night in the garage or wrap both ends of the scope in a blackout material or similar. I saw an immediate loss of tray light artifacts ensured. 

Chris

Thanks Chris, I will try that as well. Until now I was not able to take proper flats with my imaging train,

 

CS,

Janos


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