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Slow Motion and Fast Motion
When the film runs at the same speed through the camera as through the projector (for example 24 frames per second for a sound film) the movement on the screen appears as fast as the original movement in front of the camera.
For special effects the camera however may also be run at a different speed. By increasing the rate at which the film runs through the camera and projecting it at the same standard speed, the action on the screen appears to be slowed up. This so-called slow motion adds interest to sport shots as it shows the exact motions (often undetectable by the naked eye) of an athlete or a dancer. It can be used creatively to give a scene a dreamy or unrealistic effect and it is a valuable aid in industrial cinematography for analyzing rapid motion.
There the scope of this technique moves into the field of high-speed cinematography.
Some projectors can also be run at a slower speed than the standard one-for example 5 or 6 frames per second. When projected at this speed, a film shot at the normal rate appears on the screen in slow motion, though with somewhat jerky movement.
As already noted, shooting at a higher camera speed can help in making a panning movement smoother. A further use is in filming models, for example a model ship in a tank in the studio. Normally the rolling and pitching of such a ship on waves made in the tank is much too rapid to be realistic. By filming the model at a higher camera speed, the movement is slowed down to a rate where it corresponds to the motion of a real full-scale ship.
By running the camera slower than the framing rate at which the film will be projected (for example at 8 or 12 frames per second for projection at 16 or 24 f.p.s.) all movement is speeded up. This is largely used for comic effects when the shots include people. However it can also serve to heighten the apparent speed of a train or car, etc.
At a slower camera speed the exposure per frame is also increased. So this is a useful way of shooting in poor light conditions, provided no familiar movements give the show away.