A movie camera has a film like an ordinary camera. But instead of taking just one picture at a time, it takes many pictures every second.
As the film moves past the lens in the camera, a shutter continually opens and closes to give a long line of pictures on the film. Then the film is developed and shown on a screen.
Many movie cameras take a cassette of film. The cassette contains a long strip of film that lasts several minutes. It has an opening through which the film passes into the film gate. A claw mechanism pulls on the sprocket holes in the film to advance it frame by frame. The film stops in the film gate as the claw moves back, and the shutter opens briefly to expose the film. The aperture of the lens may be set by an automatic exposure control. The shutter then closes as the claw advances the film.
In many movie cameras, the shutter consists of rotating half disc. To make slow motion films, the speed of the film is increased so that more frames are exposed every second. However, the projector always runs at the same period. The film takes longer to pass through the projector than the camera, which slows down the action. Slowing down the camera speeds of the action.