[Shiraz (Ray)]

Pete

Peter may have identified the problem. I understand that Pixinsight automatically compensates for variations in chip temperature and exposure time by scaling the master dark, so bias subtraction is essential. If the SBIG cameras cannot provide bias data or if they have non-linear temperature/time profiles, the Pixinsight calibration scaling algorithm will not work properly. Not sure what you can do about it though, short of using some other software to calibrate your data, using a set of darks that exactly match the times and temperature of your light subs, as Peter suggests.