How Time-lapse Works
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, the images onscreen appear to move at normal speed.
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 freeware 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 (1992) and his feature film Baraka (1992, released to video in 2001).
Read more about this topic: Time-lapse Photography
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