A motor drive is an automatic film advance mechanism that attaches to or is built into a film camera, using an electric motor powered by batteries to automatically wind the film on to the next frame immediately after each exposure is made, cocking the shutter and readying the camera for the next shot without any manual intervention from the photographer. When the shutter button is held depressed continuously, the motor drive fires the shutter, advances the film, cocks the shutter, and fires again in rapid succession, continuing this cycle for as long as the button remains depressed or until the end of the roll of film is reached.
The motor drive was one of the most significant accessories developed for professional film cameras, transforming the ability of photographers working in action, sports, wildlife, news, and photojournalism to capture fast moving sequences of events with a continuity and completeness that manual film advance could never match. By removing the need to manually operate the film advance lever between shots - an action that requires the camera to be briefly lowered from the eye and interrupts the photographer's view of the subject - the motor drive allowed photographers to maintain continuous visual contact with the scene and keep the shutter firing at high speed throughout a critical sequence of action.
Motor drives are typically capable of advancing the film and firing the shutter at rates of several frames per second, with the fastest professional motor drive systems achieving rates of five, six, or even higher frames per second depending on the camera and motor drive model. This high speed continuous shooting capability is essential in sports and action photography where decisive moments occur and pass within fractions of a second, and where the ability to capture a rapid sequence of frames around the anticipated peak of the action significantly increases the likelihood of obtaining the single perfectly timed image within that sequence.
Motor drives were originally produced as separate accessory units that coupled to the base of compatible camera bodies via a dedicated mechanical and electrical interface, adding considerable size, weight, and cost to the camera system but providing the full range of high speed drive capabilities. Many professional camera bodies were specifically designed with motor drive coupling interfaces and were sold without a motor drive as standard, allowing photographers who did not require the high speed capability to use the camera in its lighter base configuration. Later generations of professional cameras incorporated the motor drive mechanism directly into the camera body as a built in feature, eliminating the need for a separate accessory unit and producing a more integrated and compact system. This approach of integrating the motor drive directly into the camera body has become the universal standard in modern digital cameras, virtually all of which include built in continuous shooting modes that replicate and in many cases surpass the capabilities of the fastest film era motor drive systems.