Computer simulation and geometrical construction have been used to study the contrast from twin boundaries in field‐ion micrographs. For specific orientations of the twin boundary,mrings of (hkl) planes in the matrix are expected to match withnrings of (h′k′l′) planes in the twin, wheremandnare integers and (hkl) and (h′k′l′) are prominent planes in the matrix and the twin, respectively.