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Calibrating Light Frames

18 Jul, 2018 14:20

After calibrating Light Frames I got this weird effect on the corners of the image. Is it something normal, or am I doing something wrong in the process? In the image bellow you can see the effect I am talking about and the setting I am using.

Thank you smile 
18 Jul, 2018 15:19
Hi Beck,

If we are not careful during our calibration workflow in PI, sometimes a bias might be twice subtracted which will lead to  over/under correction.
Also, problems will occur if we underexpose our flats and/or use the wrong light source . Please have a look at:

regarding image calibration, and at:

regarding flat frame acquisition.

I hope you find the above links helpful and resolve your flat issues smile
19 Jul, 2018 00:33
Because of the vignetting (effects on the corner) I would say it's a flat calibration problem. It could be that your image has no vignetting and your Masterflat has it? Also the other way around may lead to the same problem.

Also when you take flat frames you must use the exact imaging train you used to take the lights. Removing a reducer, changing its distance before taking the flats may cause this kind of problems.

And as Die Launische Diva said, a flat too dark may not provide enough vignetting correction.
19 Jul, 2018 20:33

Die Launische Diva thank you for the links. It's very

Andrea Alessandrelli looks like both of may images has vignetting.

I still really don't what can I do in order to avoid this:


20 Jul, 2018 07:42
It looks like your imaging train has so much vignetting that no light reaches the corners. If this is the case, calibrating could be a bit difficult. Did you check if your sensor is out of bounds off the lighted area?
20 Jul, 2018 10:30
Hi everybody. I just figured out how to fix it. I was not using Debayer process. I've just used and that weird effect on the corners gone away.

I really appreciate all feedback here because I was learning a lot.

Thank you all!  smile
21 Jul, 2018 14:49
If you calibrate your dark with your bias, so you can uncheck « calibrate » under your masterdark
24 Jul, 2018 01:37
astromat89 tks smile
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