[Aavso-photometry] linearity test for SBIG ST2000XM

[Gianluca]

Does anyone have results for the linearity of the ST2000XM?
I have a Newtonian 8" F/4 (800 mm focal lenght) and would like to know the maximum exposure for photometry.
I observe under urban conditions (I live in Rome) but I have never took measurements of the seeing. Does anyone know the average seeing for urban skies and tell me if correct sampling is achievable with such a camera and my scope?
Thank you very much for your help,
Gianluca (RGN)