[Aavso-photometry] linearity test for SBIG ST2000XM

[arne]

Gianluca wrote:
> 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) 

Most of the interline transfer CCD cameras like the ST2000XM, Starlight Xpress,
Meade DSI, etc. set up their gain such that you only reach about half well
on the CCD before the ADC reaches its limit.  Under these circumstances, the
CCDs are reasonably linear; they just have much smaller dynamic range
than a non-ABG camera.

The interline cameras can work ok for photometry, but would not normally
be your first choice for a photometric camera.  Richard Miles has done
very good work with the SXV-H9 camera from Starlight, but I haven't heard
of many people using the ST2000XM.  Just remember that the antiblooming
kicks in around half-well, so you need to do a linearity test such as
described in the AIP Berry/Burnell book to fully understand the conditions
under which you can use the camera effectively.
Arne