The conditions governing high resolving power in electron diffraction cameras are discussed, and, in particular, those determining the quality of resolution of the fine-structure in single-crystal reflexions. Limitation of resolution may arise from large source size, instability of electrical supplies, misalinement of the electron-optical system, interference from mechanical vibration and stray magnetic fields, grain in the photographic emulsion or too high an operating gas pressure in the camera. A camera designed to minimize these limitations is described, and its performance illustrated. Detailed fine structure, such as the subsidiary maxima of the shape transforms for small crystals, has been resolved.