35 mm movie film

35mm film with soundtracks (simulated image) (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 the late 19th century. The photographic film is cut into strips 35 millimeters wide, with six perforations per inch (25.4mm) along both edges.

The film format was introduced in still photography by Oskar Barnack, the creator of the Leica camera. In normal still photography use, the film is used horizontally, with each frame having an aspect ratio of 2:3, a size of 24 x 36 mm. The half-frame format of 18 x 24 mm was used by some still cameras in the 60's but is now obsolete.

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 35m 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, reducing the aspect ratio from an older 1.37 to 1.33. New digital soundtracks introduced since the 1990s include Dolby Digital, which is stored in two strips along the outside edges, beyond the perforations; SDDS, stored in between 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.