Slow motion video can provide new and interesting views of otherwise everyday events. This enhances their emotional impact, but also pushes the technical abilities of a camera system.
Slow motion playback starts with high-speed capture. With early film, this was called “overcranking,” since the camera operator would literally crank the film reel through the camera more rapidly. This footage would then be played back at normal frame rates — stretching time and making motion appear slower.
With digital, slow motion works much the same way, except overcranking is accomplished when the capture frame rate is faster than the playback frame rate (or “time base”). Such a camera is said to be in “varispeed” mode, and the ratio between these rates represents the amount of slow-down. If a subject were captured at 96 fps and played at 24 fps, for example, then motion would appear at quarter speed:
With RED, the suggested playback rate (or “project time base”) can be changed within the project settings menu (using the “Settings > Projects > Time Base”). Similarly, the capture frame rate can be changed using the top menu tab (as shown below). Whenever these two rates differ, the fps value at the top left will turn yellow, and the bottom right will display “Varispeed” to indicate that this mode has been successfully enabled:
See full details and examples of Slow Motion Capture on the RED 101 Article: INTRO TO SLOW MOTION VIDEO