[Aavso-photometry] Taking flats

[gianlucaros at gmail.com]

I wonder whether taking flats from a white screen pc is suitable to
take flats. I have a 17" TFT portable pc and I display a white pdf for
taking flats. I measured the brightness of the screen with the
exposure meter of a film camera and it seems even. Does anyone use
such a method for taking flats? I put the screen very close to the
telescope mouth.What if the screen does not cover the telescope mouth
precisely?
Gianluca (RGN)