Measuring electron intensity is sometimes a useful thing to do as a part of an electron microscope study. The electron intensity recorded through a sample is one of the important pieces of information needed in determining the thickness of a thin film or the molecular weight of biological structures by electron scattering methods. Modern digital imaging systems in transmission electron microscopes allow relatively easy determination of electron intensities, but some labs don't have the expensive digital systems. Photographic film has been used traditionally to record electron microscope pictures, and film can record a very high density of spatial information.