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How does a rotary shutter prevent light from reaching film while it moves?

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Director Steven Spielberg and camera operator Michael Chapman film next to a large mechanical shark on the set of the 1975 movie Jaws. — motion-picture technology Director Steven Spielberg holding the movie camera, assisted by camera operator Michael Chapman, during the filming of *Jaws* (1975).

In motion-picture technology, a rotary shutter is a mechanical device, typically shaped like a half-circle, that rotates in synchronization with the camera's film-transport mechanism.12

The shutter functions by blocking light from the lens while the film is in motion, ensuring that the film is shielded during the brief interval when it is being advanced by the claw to the next frame. Once the film is pulled into position and held motionless behind the aperture, the shutter rotates out of the way, allowing light to pass through the lens to expose the stationary frame. This precise synchronization between the shutter's rotation and the intermittent movement of the film is essential for capturing a clear, sharp image for each individual frame.123