Simulated 35mm film with soundtracks
The outermost strips (on either side) contain the SDDS soundtrack
as an image of a digital signal. In from them are the perforations
used to drive the film through the projector, along with the
Dolby Digital soundtrack between them. On the left side only
the two tracks of analog soundtrack can be seen, often encoded using
Dolby Surround to simulate a third track. Just in from the analog track
is the timecode used to synchronize a DTS soundtrack. Finally, in the center,
is the image, in this case compressed horizontally by Cinemascope
(This image is licensed for use under GFDL)
35mm film is the basic film format most commonly used for both still photography and motion pictures, and remains relatively unchanged since its introduction in 1889 by Thomas Edison. The photographic film is cut into strips 35 millimeterss wide, with six perforations per inch (25.4mm) along both edges
The origin for the 35 mm size is an Eastman Kodak 70 mm roll film for photography, being cut in two. William Kennedy Laurie Dickson, working for Edison, then cut four round perforations per frame along both edges. The format was initially called Edison size. The flattened perforations were introduced by Bell & Howell around 1900, which remain to this day for camera original film. Kodak-Standard perforations were introduced some ten years later for projection use.
A variation used by the Lumière Brothers used a single circular perforation in the centre of the film between frames.
The film format was introduced into still photography as early as 1913 (the Tourist Multiple) but first became popular with the launch of the Leica camera, created by Oskar Barnack. In normal still photography use, the film, with Kodak Standard perforations, is used horizontally, with each frame having an aspect ratio of 2:3, a size of 24 x 36 mm. See the 135 film section.
In the conventional motion picture format, frames are four perforations tall, with an aspect ratio of about 4:3. Still cameras in 35mm and the Vistavision motion picture format use a horizontal frame with is eight perforations wide, resulting in a wider aspect ratio of 3:2 and greater detail, as more film area is used per frame.
The commonly used anamorphic widescreen format Cinemascope uses the conventional four-perf frame, but an anamorphic lens is used on both the camera and projector to produce a wider image, today with an aspect ratio of about 2.35. The image as stored on the film appears horizontally compressed.
Most films today are shot and projected using the 4-perforation format, but cropping the top and bottom of the frames for a medium aspect ratio of 1.85 or 1.67. In television production, where compatibility with an installed base of 35mm film projectors is unnecessary, a 3-perf format is commonly used, giving the 16:9 ratio used by HDTV and reducing film usage by 25%.
When sound was introduced to the cinema, after some initial attempts at using synchronized record cylinders, etc., the sound started to be stored optically directly on the film. This analog soundtrack takes up a small strip to the left of the picture area. The aspect ratio of silent movies was 1:1.33. After the introduction of sound it was changed to 1:1.37 (known as standard or Academy ratio) by the Academy of Motion Picture Arts and Science.
New digital soundtracks introduced since the 1990s include Dolby Digital, which is stored in between the perforations; SDDS, stored in two strips along the outside edges (beyond the perforations), and DTS, where sound data is stored on a separate compact disc synchronized by a timecode track stored on the film just to the left of the analog soundtrack. Because all these soundtrack systems appear on different parts of the film, one movie can contain all of them and be played in the widest possible number of theaters.