LightBucket I am new to AP and don't know what tools to use to determine whether the star is saturated or to sum the pixels.
Download the FITS file from your image capture program. Then write a simple program to inspect the pixels surrounding the centroid of the star -- that lets you compute the FWHM, and gives you an idea of how far away from the centroid you should sum the pixel values to include most of the photons from the star. If the FITS file uses 16 bits, the saturated value should be 65535.
The advantage of measuring a star with known magnitude is that you can directly relate it to SQM (stellar magnitude per square arcsecond, if memory serves) if SQM is what you are looking to compute, without having to go though figuring quantum efficiency and then indirectly computing the magnitude of the background.
By the way, this should be potentially much more accurate than the "real" SQM meter since the typical telescope (even a guide scope) has a very nice narrow field of view compared to even the SQM meter with the lens. I do have an SQM-L that I use to monitor my sky brightness (19.3 for my borderline Bortle 5 and 6 sky).
Chen
