Flat overcompensating

[HSauber]

Hello,
as a newbie to PixInsight I have a difficulty with calibrating images with  flat frames.  The problem is clearly seen in the screenshot www.pisam.de/Astronomie/ttttt/ScreenshotPICal.jpg. In the raw image I have vignetting and some dark dust doughnuts which after calibration with a flat image are still visible and appear brighter as they are supposed to be. To exclude any other side effects I used only a single light frame and a single flat frame. Most likely I overlooked some detail in handling PixInsight properly.  For any hints I would be very grateful.

Herbert Sauber
Mittenwalde, Germany

[chris.bailey]

Herbert

Try adding a Master Bis frame into the calibration and tick the 'calibration' box under the master flat. Both light frames and flat frames need to be bias subtracted for the flat to work properly.

Chris

[HSauber]

Herbert

Try adding a Master Bis frame into the calibration and tick the 'calibration' box under the master flat. Both light frames and flat frames need to be bias subtracted for the flat to work properly.

Chris

Thanks Chris
This does actually improve things. But the corners of the calibrated image still look brighter as they should.

Herbert

[gvanhau]

Hello
You can try this:
http://pixinsight.com/forum/index.php?topic=9312.msg59752#msg59752

Geert

[jkmorse]

+1 on Geert's post.  Works like magic.