I am doing photometric calibration of a telescope and am trying to work out the errors on the flux that I measure. I have attempted to work out the errors due to the process of removing bias, dark frames, etc. using Poisson statistics, but this gives a fractional error of about 0.7, which is poor. I may try this analysis again using Gaussian stats, but I also want a measure of the error on the raw flux in the image (ignoring processing).
I have tried to do this by taking many observations of one star to look at the variation of flux; it roughly looks like a Gaussian, but I can't get a fit to it without altering the data.
Is there a good way to find a flux variation from data I have taken?