[konstantinos75]

Hi

I face a problem with calibration of my FIT images.

My CCD camera is SBIG ST2000XM with the following technical specs

Full Well Capacity=45.000 e- unbinned
Gain=0.6e-/ADU unbinned
saturation level=Full Well Capacity/Gain=45.000/0.6=75000 ADU


So in order to take flat frames, I adjust the exposure so the ADUs I have in the background are 75000/3=25000 for each filter.

In the attached image "master_flats" you can see the master flat frames in R,G,B,L filters.
It's obvious that the master B flat frame has more vignetting compared to the other master flat frames.

Because of this vignetting issue, the calibrated light frames are not evenly illuminated.
And as a result of this the RGB frame is not evenly illuminated, you can see the color gradients in the background.

Do you have any idea how to solve this problem?

Thank you