Negative pulldown

Negative pulldown is a characteristic of motion picture film formats. It refers to the number of film perforations that each film frame occupies, as well as whether they are pulled horizontally or vertically. The most common film pulldowns are 4-perf and 3-perf, the latter of which is usually used in conjunction with Super 35 mm film. 2-perf, used in Techniscope in the 1960s, is enjoying a slight resurgence due to the birth of digital intermediate techniques eliminating the need for optical lab work. Vertical pulldown is overwhelmingly the dominant axis of motion, although horizontal pulldown is used in IMAX, Vistavision (still in use for some visual effects work), and in consumer and professional still cameras. Most 35mm film systems, be they camera, telecine equipment, optical printer or projector, are configured to accommodate the 4-perf system, where each frame of 35mm is 4 perforations long. 4-perf was (and remains) the traditional system, and virtually all projectors are based... full article at wikipedia