The slit-scan photography technique is a photographic and cinematographic process where a moveable slide, into which a slit has been cut, is inserted between the camera and the subject to be photographed.

Use in cinematography

Originally used in static photography to achieve blurriness or deformity, the Slit-Scan technique was perfected for the creation of spectacular animations. It enables the cinematographer to create a psychedelic flow of colors which lures the spectator into an ever-changing swirl of light.

Thanks to the digital revolution, this type of effect is now created through computer animation. Slit-Scan, however, is a mechanical technique, adapted for film by Douglas Trumbull during the production of Stanley Kubrick's 2001: A Space Odyssey for the Stargate sequence. Bernard Lodge used slit-scan to create the Doctor Who title sequences from December 1973 to 1980. It requires an imposing machine, capable of moving the camera and its support. This type of effect was revived in other productions, for films and television alike.

Description

Slit-scan is an animation created image by image. Its principle is based upon the camera’s relative movement in relation to a light source, combined with a long exposure time. Everyone has seen pictures taken at night, or the long-reaching beams of light from a car’s headlights. The Slit-Scan process is similar:

1. An abstract colored design is painted on a transparent support
2. This support is set down on the glass of a backlighting table and covered with an opaque masking into which one or more slits have been carved.
3. The camera (placed high on top of a vertical ramp and decentered in relation to the light slits) takes a single photograph while moving down the ramp. The result: at the top of the ramp, when it is far away, the camera takes a rather precise picture of the light slit. This image gets progressively bigger and eventually shifts itself out of the frame. This produces a light trail, which meets up with the edge of the screen.
4. These steps are repeated for each image, lightly peeling back the masking, which at the same time produces variation in colors as well as variation of the position of the light stream, thus creating the animation.

As you can imagine, at the time of production, this effect is very expensive. A 10-second sequence requires a minimum of 240 adjustments.

External links

• Slit-Scan Photography
• Unwrapping the 2001 Slit Scan sequences
• Video of a 1974 Dr Who Slit-Scan title sequence