Filming at a reduced frame rate (6–20 fps instead of 24 fps) to create accelerated motion during normal playback; opposite of overcranking.
Technical Details
Typical undercranked frame rates range from 6 to 20 frames per second. Shooting at 12 fps and playing back at 24 fps results in double speed. Modern digital cameras offer precisely adjustable frame rates from 1 fps up to normal speed. The exposure time per individual frame is extended proportionally to the reduced frame rate, requiring corresponding adjustments to the aperture or ISO values. Variable speed motors on professional film cameras like the Arriflex 435 allow for stepless adjustment of the shooting frame rate between 1 and 150 fps.
History & Development
Undercranking originated in the 1890s with the first film cameras from Edison and the Lumière brothers. Georges Méliès systematically used this technique for magical effects in his films starting in 1896. Standardization to 24 fps only occurred with the advent of sound film around 1930 – before that, projection speeds varied between 16 and 26 fps. Modern high-end digital cameras like the RED Ranger or ARRI Alexa today offer frame rates from 0.75 fps for extreme time-lapse to several thousand fps for super slow motion.
Practical Application in Film
Classic applications can be found in silent film comedies – Buster Keaton used undercranking for acrobatic sequences, Charlie Chaplin for frantic chase scenes. In "Koyaanisqatsi" (1982), Godfrey Reggio visualizes societal acceleration through extreme time-lapse. Documentaries use 1-6 fps for cloud movements or plant growth. The workflow requires precise calculation: 30 minutes of real time shot at 2 fps results in only 2.5 minutes of footage when played back at 24 fps.
Comparison & Alternatives
In contrast to overcranking for slow motion, undercranking creates acceleration. Time-lapse photography is the modern term for extreme undercranking with intervals of seconds to hours between individual frames. Post-production speed ramping achieves similar effects digitally, but does not allow for subsequent correction of motion blur. Intervalometers control automatic long-term time-lapse recordings over days or weeks. Motion control systems synchronize camera movements with the altered time base for complex time-lapse sequences.