What is the function of rotating prism to compensate the prism in high-speed movie camera?

The motion of the film behind the lens of an ordinary film camera is not completely continuous and can be regarded as intermittent motion. It requires that the film is stationary relative to the lens at the moment when the shutter is opened, that is, the moment when the light passes. There is a mechanical shutter structure similar to Maltese cross movement in film camera, namely cam indexer. Under the operation of this mechanism, the film will pause every time it advances. At this time, the shutter is opened, the film is exposed, the shutter is closed, and then it is moved again under the traction of the tractor, and so on.

Therefore, in order to achieve high-speed photography, in principle, it is necessary to increase the frequency of intermittent motion of the film as much as possible. However, due to the mechanical structure and strength of the film, it is difficult to achieve stable intermittent motion with extremely high frequency. Even if the kinetic energy of the retractor is realized, the film will be pulled off. So the prism shutter mechanism appeared.

The prism shutter changes the motion mode of the film. After passing through a high-speed rotating prism, the film keeps moving. At this time, the film can reach a high speed of motion, and the rotation of the prism is synchronized with the motion of the film, which also compensates the picture deformation caused by the motion, thus achieving a high number of shooting frames.