Estimates of validity of projection approximation for three-dimensional reconstructions at high resolution.

As spatial frequency increases, the electron microscope "image" deviates increasingly from a true projection of the specimen's structure. This is due to the finite radius of the Ewald sphere. Quantitative estimates of these deviations of the reconstruction from the true projection are presented for a range of accelerating voltages, spatial frequencies, specimen thicknesses, and specimen tilts.