An introduction is given to the concept of colour-display systems with mechanical field-scan. The optical elements are of fundamental importance to this kind of display and various optical aspects are discussed, including the advantages of direct-viewing systems over projection, the application of cylindrical optical elements and the size of moving optical elements in relation to the required picture size. This discussion leads to the basic concept of a rotating mirror—or lens drum with a magnifying cylindrical mirror.The fundamental properties of these two solutions are compared and the favoured system with the banana tube is described in detail. The basic requirements of this system with respect to the design of the tube, the optical elements and the mechanical components are dealt with. Finally, some inherent advantages of the present system are discussed and possible further improvements are mentioned.