[en] In order to understand the detailed features in electron micrographs from radiation induced void lattices in crystals an attempt has been made to determine the contrast from columns of regularly spaced strain-free spherical voids using calculations based on the two-beam approximation. Analytical expressions have been obtained for the wave amplitudes at the exit surface of a model crystal using matrix elements. Line profiles for the contrast across a void column have been computed and two dimensional images simulated on a line printer. The contrast behaviour has been analyzed in terms of deviation from the Bragg condition for varying void column parameter: void distance/void radius. For dynamical, as well as for kinematical diffraction conditions, the influence on the image of defocusing phase contrast has been investigated by addition of extra phase contributions to the diffracted beam amplitudes. Defocusing in most cases induces an enhanced contrast from the void column. (Auth.)