Plane-wave topography is in some sense the opposite of white-beam topography, making use of monochromatic (single-wavelength) and parallel incident beam. In order to achieve diffraction conditions, the sample under study must be precisely aligned. The contrast observed strongly depends on the exact position of the angular working point on the rocking curve of the sample, i.e. on the angular distance between the actual sample rotation position and the theoretical position of the Bragg peak. A sample rotation stage is therefore an essential instrumental precondition for controlling and varying the contrast conditions.