Question about calibration

[gvanhau]

Hello
I was last night "playing" with some images taken with my QHY8L cam.
I got a strange behavior when calibrating:
If I only calibrate the images with flat frames to reduce vigneting and clean some dust particles, the resulting image resulted in a over correted one. The original darker corners an dust particles where now brighter than the rest of the image.
Curiously, I did then a try adding darks to the calibration process, and magic, the resulting frame was now evenly iluminated???
Can someone explain me why this can happen?

Regards
Geert

[Geoff]

Flat frames need a bias subtraction. Did you do this before applying them? If not, then the full calibration would have done this and hence the different result. Just a guess.