Flats from ASI 1600...
 
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Flats from ASI 1600 mm Pro don't work anymore


(@mr1337)
White Dwarf Customer
Joined: 4 years ago
Posts: 16
Topic starter  

I've tried two times reshooting flats both with short (<1sec) and longer (6sec+) exposures. The gain is definitely the same but in the final integrated image the vignetting is almost white and the image looks fine in the middle. I'm using SGP flat calibration wizard to get close to 25000 mean readout values. Any idea what would be causing the vignetting to be so bright on the edges? Could it be the driver changed the pedestal value and I need to reshoot darks?

Thanks for any pointers!

Mathew


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(@mr1337)
White Dwarf Customer
Joined: 4 years ago
Posts: 16
Topic starter  

Here are some images for reference as well if helpful. Stretched them more aggressively to show the difference in the calibration

linear single frame, 30% stretch:

linear single frame 30pct

calibrated single frame, 30% stretch:

calibrated single frame 30pct

integrated:

integrated vignetting

 


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(@rasfahan)
Hydrogen Atom Customer
Joined: 2 years ago
Posts: 1
 

Hi,

this looks like overcorrecting, I do not think your darks are at fault, this is usually an issue with your flats. I had a similar problem when I changed the USB speed value (although I cannot quite explain how that could affect things). Also, check offset and double check gain in the FITS header of your flats, darks, dark-flats (and, possibly, bias, which is not recommended to use). Posting a link to raw FITS frames would also help. You do not seem to have any dust motes in your images, so if new flats do not help or are not an option, you could try googling "synthetic flats" for a way to correct your lights for vignetting without flats. It has worked for me before with my ASI1600.


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(@mr1337)
White Dwarf Customer
Joined: 4 years ago
Posts: 16
Topic starter  

Thanks! I threw a sample of dark, flat and darkflat up and looking at their headers I noticed that just the dark has an offset value. I'm thinking that what happened was that SGP stopped supporting the existing driver that allowed offsets and now it defaults to something else (50 i believe). The newer frames don't have an offset value and I noticed the egain value was different. I will try recapturing the darks tonight and will repost if that solved the issue. Fingers crossed!

 

 


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(@mr1337)
White Dwarf Customer
Joined: 4 years ago
Posts: 16
Topic starter  

Just closing the loop for anybody searching for this in the future - that was definitely the issue. Finally getting calibrated images again, thanks for the help!


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

Excellent find! These can be hard to get at.


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