It is not necessary for a documentary maker fully to understand the physical processes by which the raw material—the images and sounds—are captured and converted into permanent records, ready for editing into the final film. It is enough for a director to know what he or she wants, rather than the precise details of how to achieve it. The cine-photographer and the sound recordist will have the technical expertise to realize the director’s vision. But when planning and designing scenes for a film, some appreciation of the technicalities can be useful in helping to make plain what is, and what is not, possible. The director should have enough knowledge to ensure that the vision is one which is capable of realization. Every film-maker should know at least something in principle of how the lens and the microphone do their work.