When we look at a frame, the brain registers its image, which stays for a short while even after the frame has been removed. This physiological phenomenon is called the ‘persistence of vision’. If at least 12 such frames appear in a series before our eyes per second, a psychological illusion is created that forms the basis of motion picture. Ingmar Bergman called this phenomenon as a ‘defect’ of human visual process. But thanks to this ‘defect’ that the art of moving image was born.
FPS or Frames-per-Second is the number of frames exposed during shooting from a movie camera. It can also mean the number of frames projected from the movie projector. During the silent era, films were shot and projected at 16-18 FPS. But as the Talkies arrived, 24 FPS became the norm. This current standard is also called ‘sound speed’ and it is this FPS at which your TV or even your Laptop shows you the images. Thus, the silent films which were shot at 16-18 FPS look speeded-up. Chaplin’s comedy appears more comical today than to its original audience!
If shooting is done at 240 FPS, while being projected (at 24 FPS) the action seems to be taking ten times more time than normal. This is the basis of Slow Motion Photography. Similarly, to achieve Fast Motion, camera allows exposure of frames at a lesser rate, say 3 FPS, which on projection appears eight times faster. Also, you must have seen shots of Extreme Fast Motion or Time Lapse Photography in which a night sky gives way to morning, the sun rises and it is day – all in a matter of seconds. It is achieved by allowing camera to expose frames intermittently, say 1 frame per minute. When the series of frames is run at the ‘sound speed’, the desired result is achieved.
The modulation of FPS has made Motion Picture Camera play with time the way a microscope or a telescope plays with space to enable visual perception beyond human capacity. And going beyond the scientific study, it has revealed the psychological effect of altered sense of motion, resulting in the now-cliché slow motion love scenes, and more. Next time a movie moves you, thank the moving FPS.