Apple Final Cut Pro 7 - Manual (Page 1920)

Early television systems selected frame rates based on local electrical standards to avoid
electrical interference with the picture. NTSC in North America uses 30 fps (now adjusted
to 29.97 fps for color NTSC) based on 60 Hz electrical power. PAL, used primarily in Europe,
uses 25 fps based on 50 Hz electrical mains.
Because film cameras are relatively simple compared to video cameras, they allow shooting
and playing back with a wide range of frame rates (although the standard projection
speed is 24 fps). Video formats are much less flexible, partly because of their electronic
complexity and partly because a television is designed to play video at only one frame
rate. However, as video technology evolves, many digital camcorders now offer several
frame rate choices while maintaining compatibility with existing NTSC and PAL video
systems.
One second
60 fps
24 fps
Understanding Flicker and Perceived Frame Rate
Movie screens are not constantly illuminated, although when you watch a movie in the
theater, it appears that this is the case. A film projector’s shutter actually blocks the light
to the screen when each frame advances, but your eyes momentarily retain the image
until the shutter opens again (thanks to persistence of vision).
When you close your eyes, there is a brief moment when you can still see what you were
looking at, especially if what you were looking at is quite bright compared to the
surrounding environment. This persistence of vision is so brief that you may not be
consciously aware of it, but it is this phenomenon that allows us to believe that rapidly
changing still images are moving continuously.
However, the higher the frame rate, the more film you need, the faster the projector must
operate, or the more electronic bandwidth you need (in the case of video). Early audience
perception tests with movies demonstrated that increasing the rate of flicker increased
the perception of smooth motion, even if the images themselves were not changing
during every single flicker. The perceived frame rate (or flicker rate) can be increased by
opening and closing the projector’s shutter two or three times for each film frame, creating
a less noticeable flicker onscreen. Therefore, even though movies are universally shown
at 24 fps, the projector’s shutter may open and close at 48 fps, or perhaps higher.
1920 Appendix C Frame Rate and Timecode