A digital Micrograph script that acquires a series of images at different exposure times and combines them into one, producing data like that shown below, is available here.
Before collecting any data make sure that your camera can cope with the intensity of the electron beam without being damaged. Repairs to the camera can be very expensive and none of your colleagues will be happy if all of their pictures have a spot in the middle. I am happy to give advice on good procedure, send me an email r dot beanland at warwick dot ac dot uk.
Here is a line plot through the data - note the log scale!