Apple Final Cut Pro 7 - Manual (Page 1921)

Early television systems used a different approach for the same result: increased flicker
without increasing the necessary electronic bandwidth. Interlaced scanning fills a television
frame with only half the video lines of a frame (this is known as a field), and then fills in
the remaining lines (the other field). A field effectively fills the television screen with an
image, even though it is only half-resolution, and it does so in half the time it would take
to draw the full frame. The result is a perceived frame rate which is double the actual
frame rate. For NTSC, the frame rate is 29.97 fps, but the perceived frame rate (the field
rate) is 59.94 fps. This causes less flicker. PAL, which has a lower frame rate of 25 fps (or
50 fields per second) has a slightly more noticeable flicker.
How Many Frames per Second Is Best?
When recording an object in motion, there are practical reasons to limit the camera frame
rate:
• The limit of human perception: There is no reason to show more frames per second than
the viewer can perceive. The exact limit of human motion perception is still up for
scientific debate, but it is generally agreed that there is an upper threshold after which
people can’t appreciate the difference.
• Media cost and size: Film and videotape stock cost money. Higher frame rates require
more footage and are more expensive to shoot. Editing and media management
become more difficult as the amount of raw media increases.
Recording High Frame Rates for Slow-Motion Effects
Despite the increased cost and effort, there are cases where shooting higher frame rates
is useful. Slow-motion effects are created by recording hundreds of frames per second
and then playing the same frames back at a slower rate. For example, a bullet shattering
a light bulb may take only a fraction of second, seeming almost instantaneous to anyone
watching. If a camera records the light bulb a thousand times per second and then a
projector plays the frames back at 24 fps, the movie onscreen will take almost 40 times
as long (1000 fps ÷ 24 fps = 41.6 seconds). The higher the frame rate, the more temporal
(time) resolution your footage has, which means it can be slowed down to show detailed
moments that would otherwise be a blur. Shooting at high frame rates also requires more
light, because there is less time to expose each frame.
Recording Slow Frame Rates for Time-Lapse Photography
Slow frame rates are used for time-lapse photography, in which a scene is recorded
relatively slowly, perhaps one frame every second, hour, or day. This is useful when you
are trying to capture gradually changing events, such as growing plants, the movement
of clouds, or the rising and setting of the sun. When played back at standard frame rates,
events occur rapidly onscreen and otherwise undetectable patterns emerge.
1921 Appendix C Frame Rate and Timecode