Accelerated-motion Photography

filming with less frequent frame changes than the normal projection speed (16 or 24 frames a second).

Accelerated-motion photography uses regular movie equipment that has an electric motor equipped with a rheostat to regulate the speed at which the film moves through the gate. Thus the camera attains a minimum speed of two to three frames a second. For greater retardation an electric motor with a controllable adaptor is installed on the camera to permit uninterrupted shooting at speeds ranging from one frame a second to one frame every four seconds.

Accelerated-motion photography is used in trick shots to heighten the sense of speed (in chases, leaps, and dangerous or risky action) and in scientific or educational films to accelerate a slow process whose movement is not visible to the naked eye. Since the reduced frequency of frame changes brings about an inversely proportional greater exposure, this technique is used with insufficiently-lit still objects.

Particularly slow processes (such as the growth of a fetus or plant) are filmed with time-lapse photography, with specific (long) intervals between frames, during which the electric motor is switched off.