Abstract

The standard symmetry tables for convergent-beam diffraction are for the case o the zero-order Laue zone. However, the symmetries oí reflections in the higher-order Laue zone are in general different from the symmetries of the reflections in the zero-order Laue zone. Four symmetry operations produce symmetry relations for reflections in the zero-order Laue zone only, the corresponding symmetry operations are missing in reflections in higher-order Laue zones. Twenty-one of the 31 diffrac­tion groups has oneór more of these four operations (alone or in combination with other symmetry op­erations). The four operations are those operations that exchange “up” and “down”; they are an inver­sión center, a horizontal mirror, a horizontal two-fold axis, and a four-fold inversión axis. Despite the difference between the symmetries of zero-layer and higher-order-Laue-zone reflections, the pattern symmetries of on-axis convergent beam patterns are unmodified