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Film technique where the frame rate is lower than that used to view the sequence

Time lapse photography is a technique in which the frequency at which film frames are captured (the frame rate) is much lower than the frequency used to view the sequence. When played at normal speed, time appears to be moving faster and thus lapsing. For example, an image of a scene may be captured at 1 frame per second but then played back at 30 frames per second; the result is an apparent 30 times speed increase. Similarly, film can also be played at a much lower rate than at which it was captured, which slows down an otherwise fast action, as in slow motion or high speed photography. Processes that would normally appear subtle and slow to the human eye, such as the motion of the sun and stars in the sky or the growth of a plant, become very pronounced. Time lapse is the extreme version of the cinematography technique of undercranking. Stop motion animation is a comparable technique; a subject that does not actually move, such as a puppet, can repeatedly be moved manually by a small distance and photographed. Then, the photographs can be played back as a film at a speed that shows the subject appearing to move.

The frame rate of time lapse movie photography can be varied to virtually any degree, from a rate approaching a normal frame rate (between 24 and 30 frames per second) to only one frame a day, a week, or longer, depending on subject. The term "time lapse" can also apply to how long the shutter of the camera is open during the exposure of each frame of film (or video), and has also been applied to the use of long shutter openings used in still photography in some older photography circles. In movies, both kinds of time lapse can be used together, depending on the sophistication of the camera system being used. A night shot of stars moving as the Earth rotates requires both forms. A long exposure of each frame is necessary to enable the dim light of the stars to register on the film. Lapses in time between frames provide the rapid movement when the film is viewed at normal speed. As the frame rate of time lapse approaches normal frame rates, these "mild" forms of time lapse are sometimes referred to simply as fast motion or (in video) fast forward. This type of borderline time lapse resembles a VCR in a fast forward ("scan") mode. A man riding a bicycle will display legs pumping furiously while he flashes through city streets at the speed of a racing car. Longer exposure rates for each frame can also produce blurs in the man's leg movements, heightening the illusion of speed. Two examples of both techniques are the running sequence in Terry Gilliam's The Adventures of Baron Munchausen (1989), in which a character outraces a speeding bullet, and Los Angeles animator Mike Jittlov's 1980s short and feature length films, both titled The Wizard of Speed and Time. When used in motion pictures and on television, fast motion can serve one of several purposes. One popular usage is for comic effect. A slapstick comic scene might be played in fast motion with accompanying music. (This form of special effect was often used in silent film comedies in the early days of the cinema; see also liquid electricity). Another use of fast motion is to speed up slow segments of a TV program that would otherwise take up too much of the time allotted a TV show. This allows, for example, a slow scene in a house redecorating show of furniture being moved around (or replaced with other furniture) to be compressed in a smaller allotment of time while still allowing the viewer to see what took place. The opposite of fast motion is slow motion. Cinematographers refer to fast motion as undercranking since it was originally achieved by cranking a handcranked camera slower than normal. Overcranking produces slow motion effects.

Film is often projected at 24 frame/s, meaning 24 images appear on the screen every second. Under normal circumstances, a film camera will record images at 24 frame/s since the projection speed and the recording speed are the same. Even if the film camera is set to record at a slower speed, it will still be projected at 24 frame/s. Thus the image on screen will appear to move faster. The change in speed of the onscreen image can be calculated by dividing the projection speed by the camera speed. So a film recorded at 12 frames per second will appear to move twice as fast. Shooting at camera speeds between 8 and 22 frames per second usually falls into the undercranked fast motion category, with images shot at slower speeds more closely falling into the realm of time lapse, although these distinctions of terminology have not been entirely established in all movie production circles. The same principles apply to video and other digital photography techniques. However, until very recently , video cameras have not been capable of recording at variable frame rates. Time lapse can be achieved with some normal movie cameras by simply shooting individual frames manually. But greater accuracy in time increments and consistency in exposure rates of successive frames are better achieved through a device that connects to the camera's shutter system (camera design permitting) called an intervalometer. The intervalometer regulates the motion of the camera according to a specific interval of time between frames. Today, many consumer grade digital cameras, including even some point and shoot cameras have hardware or software intervalometers available. Some intervalometers can be connected to motion control systems that move the camera on any number of axes as the time lapse photography is achieved, creating tilts, pans, tracks, and trucking shots when the movie is played at normal frame rate. Ron Fricke is the primary developer of such systems, which can be seen in his short film Chronos (1985) and his feature films Baraka (1992, released to video in 2001) and Samsara (2011).

Time lapse can be combined with techniques such as high dynamic range imaging. One method to achieve HDR involves bracketing for each frame. Three photographs are taken at separate exposure values (capturing the three in immediate succession) to produce a group of pictures for each frame representing the highlights, mid tones, and shadows. The bracketed groups are consolidated into individual frames. Those frames are then sequenced into video.

Day to night transitions are among the most demanding scenes in time lapse photography and the method used to deal with those transitions is commonly referred to as the "Holy Grail" technique.