Camera technique that dynamically adjusts frame rate during recording (1–120 fps on systems like ARRI Alexa 35) to achieve seamless time-remapping effects in-camera without post-production.
Technical Details
In 2007, the RED One introduced true Variable Frame Rate as the first cinema camera, offering a spectrum from 1 to 60 fps. Current systems like the ARRI Alexa 35 achieve 1-120 fps at 4K resolution, and the Sony FX9 manages 1-180 fps in Super35. The change is achieved through electronic shutter control and adjusted sensor readout. Ramping modes enable smooth transitions between frame rates over defined periods of 2-30 seconds. The camera mathematically interpolates intermediate values and automatically adjusts exposure time and ISO to changing light levels.
History & Development
In 1985, Phantron developed the first mechanical Variable-Speed camera for 16mm film, with a range of 6-150 fps. The digital era began in 2005 with the Silicon Imaging SI-2K, which offered software-based frame rate changes from 1-30 fps. In 2008, the RED Scarlet expanded the spectrum to 1-300 fps. ARRI followed in 2010 with the Alexa series (1-60 fps), and Sony in 2019 with the FX9 (1-180 fps). Current high-end cameras like the Phantom TMX 7510 reach over 1.75 million fps at reduced resolution.
Practical Application in Film
Christopher Nolan utilized Variable Frame Rate in "Dunkirk" (2017) for seamless transitions between timelines – from 24 fps to 48 fps for aerial combat sequences. "Mad Max: Fury Road" (2015) switched from 24 to 48 fps during car chases for increased clarity in fast-moving action. The workflow requires specialized post-production software like DaVinci Resolve or Avid Symphony, which automatically correct timecode discrepancies. Disadvantages arise from more complex audio synchronization and increased data volumes at higher frame rates.
Comparison & Alternatives
Variable Frame Rate differs from High Frame Rate (HFR) by the ability to change within a single shot, whereas HFR refers to consistently high frame rates. Speed ramping as a post-production technique creates similar effects through time manipulation but does not achieve the organic quality of true frame rate changes. Phantom high-speed cameras offer extreme frame rates up to 12 million fps, but without variable functionality during recording.