We investigate coherent diffraction patterns from an amorphous SiO \(_2\) across a range of electron counting regimes, from sparse single-event detection to cumulative high-flux exposures. Low electron count rates, with a mean of approximately 0.017 electrons per pixel, reveal discrete electron events dominated by shot noise. In contrast, cumulative patterns acquired over 60 s exhibit pronounced speckle features reflecting atomic arrangements in the material. The count contrast \(C_k\) as a function of mean electron count \(\overline{K}\) transitions from a Poisson-dominated \(1/\sqrt{ \overline{K} }\) trend at low \(\overline{K}\) to a stabilized \(C_k = 0.23\) beyond \(\overline{K} = 10\) , of which behavior is modeled effectively with a spatial degree of freedom \(M = 32\) . This M value indicates partially coherent illumination, deviating from single-mode expectations of the electron beam. Our finding bridges a gap between statistical optics and applied TEM and introduces a framework with direct practical relevance for modern detector technologies.
