Electron crystallography of thin three-dimensional (3D) protein crystals requires very exact determination of tilt angles and spot profiles to obtain correct merging of diffraction spot amplitudes. The reciprocal lattice of 3D microcrystals consists of ellipsoidal spot profiles which are very extended in the direction normal to the crystal face (z*). To extrapolate from the intensity measured in a section to the total spot intensity, two features need to be known very exactly: 1. the orientation of reciprocal lattice relative to the Ewald sphere, 2. the 3D-shape of the spot cloud.

Fig. 1 shows a tilt series of one frozen hydrated catalase crystal, in the order of recording. The third diffraction pattern gives the highest resolution because it is untilted and therefore the electrons have the shortest path length. In the current experimental data taken at 120 keV electron energy inelastic scattering within the crystal leads to a dramatic loss of elastic information in highly tilted patterns.