movie camera

Principle of operation

A movie camera creates the impression of motion by recording a scene not once but as a rapid, evenly spaced series of still images called frames. Light from the scene enters through the lens, which forms an image at the plane of the recording medium. A shutter admits that light for a measured interval, then closes; during the closed phase the medium is advanced or read out so that the next frame captures a slightly later instant. Played back at the same rate at which they were taken, the frames fuse into apparently continuous movement. The rate at which frames are recorded is the camera’s frame rate, and the exposure of each frame is governed jointly by the lens aperture, the shutter interval, and the sensitivity of the medium.

Core components

Several systems are common to movie cameras regardless of medium. The lens mount is a standardized mechanical and optical interface that holds the lens at a fixed distance from the recording plane and allows lenses to be interchanged. The shutter times each exposure and blocks light while the medium advances or is read. The film gate, in a film camera, is the aperture that holds each frame flat and steady during exposure; in a digital camera this position is occupied instead by the image sensor. A viewfinder lets the operator see and compose the field being recorded, historically by diverting part of the incoming light through a reflex mirror and today often through an electronic display. Finally, a transport or recording system moves the medium: a mechanical camera pulls perforated film through the gate frame by frame, while a digital camera converts the sensor’s output into data written to a memory card or drive.

Film and digital cameras

The chief division among movie cameras is between those that record on film and those that record with an electronic sensor. A film camera exposes a light-sensitive emulsion on a strip of photographic film; a claw or registration pin engages the film’s perforations and advances it intermittently, holding each frame motionless in the gate while the shutter is open. The exposed film carries a latent image that must be chemically developed before it can be seen. A digital camera replaces the film and gate with an image sensor that converts the projected light into electrical signals, which are digitized and stored as image data. Digital capture allows immediate review and eliminates chemical processing, and the sensor’s fixed dimensions take the place of the film format in setting the area recorded behind a given lens. Both kinds share the same underlying task of registering a timed sequence of frames, and both are operated within the broader craft of filming.