Flikipedia A branching dictionary of the moving image

shutter

/ˈʃʌtər/ noun

The mechanism that controls how long each frame is exposed to light and blocks the light while the film advances or a sensor reads out. Its open interval, together with the frame rate, sets both exposure and the amount of motion blur recorded in each frame.

Origin From shut (Old English scyttan, “to bar, close”) plus the agent suffix -er; a shutter is literally a thing that shuts. The photographic sense — a device that opens to admit light for a measured time — dates to the mid-19th century.

  1. Cinematography In a motion-picture camera, a rotating opaque disc with an open sector that alternately admits light to the frame and blocks it. While the disc is closed the exposed frame is pulled clear and the next unexposed frame is registered in the gate, so that film advances only in darkness.

  2. Exposure The interval, expressed as a fraction of each frame's duration, during which light reaches the film or sensor. On a rotary shutter this is described by the shutter angle — the angular width of the open sector — and it determines the exposure time and the length of motion blur.

  3. Image sensors In a digital camera, the electronic control of when each photosite begins and ends collecting charge. A global shutter exposes and reads the whole sensor at once; a rolling shutter exposes and reads it row by row, so different parts of the frame correspond to slightly different instants. rolling-shutter skew in a fast pan

The rotary disc shutter

In a mechanical motion-picture camera the shutter is an opaque disc with a cut-away open sector, spinning in step with the film transport. As the open sector passes the gate, light from the lens reaches the stationary frame and exposes it; as the solid portion follows, the frame is covered and the mechanism pulls the exposed frame away, advancing the next one into position. Because film moves only while the gate is dark, the shutter both meters the exposure and hides the transport of the strip. The same disc governs a projector, where its closed phase conceals the movement of each frame into place and can subdivide the dark interval to raise the flicker rate above the threshold of visible flicker.

Shutter angle and motion blur

The fraction of each frame period during which the shutter is open is described by its angle: a disc with a 180° opening is open for half of each cycle, so at any given frame rate the exposure lasts half the interval between frames. A wider angle lengthens the exposure and admits more light but records more movement within a single frame, producing longer motion blur; a narrower angle shortens the exposure and freezes motion into distinct, sharper images. The 180° setting is a common reference, tying exposure time directly to frame rate — for example, a forty-eighth of a second at twenty-four frames per second. Shutter angle and frame rate together therefore determine how continuous or stroboscopic recorded movement appears.

Electronic shutters in image sensors

A digital image sensor has no moving disc; exposure is controlled electronically by when each photosite starts and stops accumulating charge. A global shutter exposes every photosite over the same interval and reads the whole array at once, so the entire frame corresponds to a single instant. A rolling shutter exposes and reads the sensor progressively, one row after another, so the top and bottom of a frame are captured at slightly different times. During fast subject motion or rapid camera movement this time offset can skew, wobble, or smear straight edges. As with a mechanical shutter, the electronic exposure interval sets both the brightness of the frame and the amount of motion blur it contains.

See also

  • frame rate— The number of frames shown per unit of time, given in frames per second (fps), which governs how smoothly motion is rendered and how strongly a projected or displayed image flickers.
  • exposure— The quantity of light reaching the film or sensor while an image is recorded, and the act of admitting it — governed jointly by aperture, shutter, and sensitivity.
  • image sensor— The electronic component that captures a digital image, converting light into electrical charge at a grid of photosites — the digital counterpart to photographic emulsion.
  • frame— A single still image in a film strip or digital video stream; the basic unit of the moving image, from which a motion picture is built by rapid succession.

Sources

  1. Society of Motion Picture and Television Engineers (SMPTE)
  2. Kodak, "The Essential Reference Guide for Filmmakers"
  3. Nakamura (ed.), "Image Sensors and Signal Processing for Digital Still Cameras"

Last revised: September 18, 2026