35 millimeter/7O mm: This is referring to the total width of the film strip from side to side or edge to edge, measured in millimeters.
Perf/Perforations: Holes near the edges of the film that movie cameras and projectors use to advance the film to the next frame. Different formats and sizes of film use different numbers of perforations per frame. Perf size and distance is standard on all formats.
Picture Area: The dimensions and area of the actual space on the film strip used for visual information being captured or shown for each frame.
Film Grain: The photosensitive chemical elements of film that can represent light and picture information, similar to digital “pixels” but not directly comparable.
Why are these terms important?
These basic concepts and definitions are important to understanding the nature and qualities of movie film because of the basic rule that there is a physical limit to how much picture information can physically exist in a defined area of film. The larger the picture area is on the film, the less magnification is needed by the projector lens to fill the screen, and thus the projected image will look sharper the viewer due to more picture information physically existing on the film. For example, if a 1”x1” area can hold a picture consisting of 1000 film “grains”, than a 2”x2” area could hold four times that much, or 4000 “grains,” meaning that you are getting 4 times the picture quality on the same size movie screen, or you can get the same picture quality on a screen 4 times as large as a standard screen.
35MM Film: The standard of moviemaking and projection since the beginning of the motion picture industry in the late 19th century. This size of film, measured 35mm edge to edge, became an official standard in 1909. For sound movies (“talkies”) there is a dedicated soundtrack area included on the movie film as well as the picture area, which results in there being less useable space for the picture, as soundtracks and the pictures compete for physical space. On modern movie films, the actual picture area is 21.95mm wide and 16mm tall. There are perforations in the film every few mm, making each frame of the movie 4 perforations tall. 35MM film has multiple types of soundtracks included on the film itself, and can also be supplied with a separate CD that synchronizes with a sequence of dots printed to the film called a “timecode”. There are generally 4 types of sound that can be used with 35mm film, DD (Dolby Digital), an Analog waveform, SDDS (Sony Dynamic Digital Sound), and DTS (Dedicated To Sound). The most commonly used is Dolby Digital, followed by DTS, as both are capable of storing data for the now ubiquitous 5.1 surround systems.
7OMM Film: A premium film format that was used for large budget movies, primarily used from the 1950s to the 1980s, as it had a lot higher quality picture compared to 35mm; it was able to project onto larger screens, and allowed for surround sound before 35mm was capable. 7Omm film has seen use in a small number of movies in the 90s and 2000s, but since digital projection and sound became the norm it has fallen out of use completely until very recently. There has been a resurgence in its use again in the past few years with the filming of “Samsara,” and select scenes from “Inception.” It was used for the filming and projection in select theatres for “The Master” and “The Hateful Eight.” The actual picture area is 48.5x21mm, which is nearly 3 times the picture area compared to 35mm film; this means it had 3 times the amount of grains and thus, picture quality. 7OMM film use a picture that is 5 perf tall, as opposed to the 35MM 4 perf high picture, and 7OMM film had magnetic strips on the sides of the picture area and perforations for the soundtrack. The magnetic soundtrack uses the same technology as a cassette tape, but a much higher quality. On modern 7Omm systems, magnetic soundtracks are no longer used due to the toxic and environmentally damaging chemicals used in their production. Now digital sound is used, DTS and DTS “Special Venue.” Soundtrack technologies on 7Omm film are all capable of 6 tracks or channels, either 5 screen channels and 1 surround, or the modern format of 3 screen channels, two surround, and a subwoofer (5.1 surround).
IMAX 7OMM: IMAX film is the largest film ever used for movies. It uses the same film as the previously covered 7Omm, but instead of the film running vertically through a projector as is standard for 35mm and 7Omm, IMAX 7Omm runs horizontally through the camera and projector. The picture area is 68x52mm, 15 perf wide; almost 4 times the picture area of 7OMM, and 10 times the picture area of 35MM. Sound for IMAX is a special 6 channel mix - played from a CD or hard drive. There is no sound on the film itself, the projector has a mechanism that counts how many frames have been played and the sound player synchronizes to that. IMAX sound is different from 35mm and modern 7Omm in the fact that every channel has the full range of sound including a subwoofer to play low frequencies and bass in surround. In the center there are two speakers arranged one on top of the other, instead of a traditional single speaker, this gives a sense of height in the sound for effects like rain, flyovers, and naturally, rocket and shuttle launches.