The general equation for the effective region of doubly curved diffractors for radiation from a point source that was derived by Wittry and Sun [J. Appl. Phys.71, 1 (1992)] has been extended to include the effect of source misalignment. Intensity profiles across an x‐ray topograph recorded on a photographic film located between the diffractor and the focus have been calculated for the Johann case including misalignment effects. Topographs and intensity profiles obtained using TiK&agr; radiation generated by a focused electron beam have confirmed the theoretical calculations and have provided values of the peak reflectivity and rocking‐curve width for graphite, mica, and silicon diffractors of Johann geometry with a radius of curvature of ∼100 mm.