Negative pulldown

3-perf is a 35mm film camera system used only in the origination and post-production transfer process. Typically, most 35mm film systems, be they cameras, telecine equipment, optical printers, or projectors, are configured to accomodate 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 on 4-perf, because 4 perforations is the amount needed per frame vertically in order to have enough negative space for a roughly squarish image, which became the silent film standard aspect ratio of 1.33. Later, when the film industry was facing the perceived threat of obsolescence to television, which also was universally a 1.33 aspect ratio at the time, studios started experimenting with various competing widescreen formats.

Eventually, aspect ratios of 1.85 in North America and 1.66 in Europe became standard for 35mm productions shot with normal non-anamorphic lenses. However, the way the aspect ratio is created with these films is not in-camera, but rather by placing a cropping device, known as an aperture mask, over the film in the projector. What this means is that most films are shot in full screen format (what we call 1.33 but actually is 1.37 because of the sound tracks), but composed for 1.85 or 1.66 and cropped that way in projection. Therefore, a fair percentage of the film is wasted, because the cropped top and bottom aren't ever meant to be shown.

What 3-perf does is solve this wastage problem by changing the camera gate and shutter mechanism so that each frame is 3 perforations long. The three perf image is very close to 1.85 without having a perforation worth of wasted unused image. Because of this, the same amount of film footage will give 25% more shooting time, saving money on film stock; the camera will run quieter because less film is moved through the camera per frame; and all of the negative image is used to create a widescreen image without the need for anamorphic lenses, which typically require more light and give less depth of field than their equivalent normal spherical lenses.

The only disadvantage of 3-perf is that if it is to be projected theatrically, it needs to be transferred back to a 4-perf system, which typically means a film print with black cropping on the print itself in order to fit the 3-perf image onto a 4-perf frame - the same wastage problem as before. Even so, the amount of film shot on a production is much greater than the length of the final film, so 3-perf still is a viable cost-saving option for production. Generally, therefore, 3-perf is most frequently used for widescreen television productions shot on film, because the film will be developed and then transferred to video, rendering projection incompatibilities irrelevant.

Recently, noted cinematographer Vittorio Storaro has come out in favor of a film standard known as Univision (alternately sometimes called Univisium), which advocates 3-perf Super 35mm to create a 2:1 aspect ratio.