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Flats not working correctly for some reason

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#1 Scdouglas

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Posted 11 April 2021 - 05:39 PM

So I've been having issues like the one shown below for a bit now where the flat creates this dark patch in the lower right side. Ignore the top left because I have flats that remove that correctly, the ones shown just happen to not, but the bottom right is still really bad. I use the white t-shirt over my scope and use the NINA flat automation tool so I'm not really sure what's happening. It's also worth mentioning the dark patch is always in the bottom right, doesn't matter what DSS settings use or what time of day I take the flats. 

 

Could this be light leak in the flat acquisition process? Something I'm not thinking of. I used to take flats all the time for my Canon T3i and it was never an issue, but I have yet to take a successful flat with my ASI1600MM. This was always a pretty straight forward process so I'm a little annoyed by this after about 4 different attempts. Anyone got any ideas? 

 

Edit: I should also note that this image is a screenshot of the DSS output with the black point brought in a bit for contrast. 

 

flat.JPG


Edited by Scdouglas, 11 April 2021 - 05:39 PM.


#2 Stelios

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Posted 11 April 2021 - 08:15 PM

Can't really tell from that. Can you post an uncalibrated light and a stretched flat? 

 

Are you using an OAG? 



#3 Scdouglas

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Posted 11 April 2021 - 09:08 PM

Can't really tell from that. Can you post an uncalibrated light and a stretched flat? 

 

Are you using an OAG? 

Sure thing, the two files are linked below. The light was a 2 minute sub captured just the other night with my green filter. I already know there is some vignetting, I'm at F4 with 1.25" filters (upgrading soon, it's what I have right now). I never thought to check a stretched flat before so maybe this will solve it. Also I'm not using an OAG, the only thing between the sensor and mirror is a coma corrector. 

 

After looking at the flat, are those dark spots just bad application of the t-shirt? You can see sort of blobs of dark spots on the flat and it clearly isn't an even light field so I think that might be it. Thoughts? 

 

Files: 

Uncalibrated light: https://www.dropbox...._0066.fits?dl=0

Stretched flat: https://www.dropbox....d flat.png?dl=0




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