The form of the dynamical theory normally used in calculations of diffraction contrast is based on the assumption of symmetrical Laue diffraction conditions. The results of previous investigations have shown this assumption to be valid for angles between the surface normal and the Brillouin zone boundary of up to 70°. The results presented in this paper show that although this is true for strong‐beam diffraction conditions, the error involved in calculations based on the assumption of symmetrical Laue diffraction conditions increases significantly as the deviation from the Bragg condition of the strong beam increases. In weak‐beam diffraction conditions significant differences between the symmetrical and non‐symmetrical Laue cases are obtained for angles between the surface normal and the zone boundary as small as 30°. This is verified by calculations of both diffracted beam intensities and dislocation profiles. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA
