The process of speeding the frame rate of a camera up, so that when the captured pictures are played at the normal frame rate the action appears to be in slow motion. The term originates from early film cameras that employed a crank handle to roll film.
Slow-motion (commonly abbreviated as slo-mo or slow-mo) is an effect in film-making whereby time appears to be slowed down. It was invented by the Austrian priest August Musger in the early 20th century.
Typically this style is achieved when each film frame is captured at a rate much faster than it will be played back. When replayed at normal speed, time appears to be moving more slowly. A term for creating a slow-motion film is overcranking which refers to hand cranking an early camera at a faster rate than normal (i.e. faster than 24 frames per second). Slow-motion can also be achieved by playing normally recorded footage at a slower speed. This technique is more often applied to video subjected to instant replay than to film. A third technique that is becoming common using current computer software post-processing (with programs like Twixtor) is to fabricate digitally interpolated frames to smoothly transition between the frames that were actually shot. Motion can be slowed further by combining techniques, interpolating between overcranked frames. The traditional method for achieving super-slow motion is through high-speed photography, a more sophisticated technique that uses specialized equipment to record fast phenomena, usually for scientific applications.
Slow-motion is ubiquitous in modern filmmaking. It is used by a diverse range of directors to achieve diverse effects. Some classic subjects of slow-motion include:
Athletic activities of all kinds, to demonstrate skill and style.
To recapture a key moment in an athletic game, typically shown as a replay.
Natural phenomena, such as a drop of water hitting a glass.
Slow-motion can also be used for artistic effect, to create a romantic or suspenseful aura or to stress a moment in time. Vsevolod Pudovkin, for instance, used slow motion in a suicide scene in The Deserter, in which a man jumping into a river seems sucked down by the slowly splashing waves. Another example is Face/Off, in which John Woo used the same technique in the movements of a flock of flying pigeons. The Matrix made a distinct success in applying the effect into action scenes through the use of multiple cameras, as well as mixing slow-motion with live-action in other scenes. Japanese director Akira Kurosawa was a pioneer using this technique in his 1954 movie Seven Samurai. American director Sam Peckinpah was another classic lover of the use of slow motion. The technique is especially associated with explosion effect shots and underwater footage.
The opposite of slow-motion is fast motion. Cinematographers refer to fast motion as undercranking since it was originally achieved by cranking a hand-cranked camera slower than normal. It is often used for comic, or occasional stylistic effects. Extreme fast motion is known as time-lapse photography; a frame of, say, a growing plant is taken every few hours; when the frames are played back at normal speed, the plant is seen to grow before the viewer's eyes.
The concept of slow-motion may have existed before the invention of the motion picture: the Japanese theatrical form Noh employs very slow movements.
For the purposes of making the above illustration readable a projection speed of 10 frames per second (frame/s) has been selected, in fact, film is usually projected at 24 frames/s making the equivalent slow overcranking rare, but available on professional equipment.