Rotating Mirror cameras use a mirror which spins at very high speeds driven by a gas turbine. Mirrors rotate at up to 20,000 revolutions per second (1.2 million rpm). The mirror is most often made from a beryllium substratum with an aluminum overcoat. Beryllium is chosen because it is one of the few known materials with strength-to-weight characteristics high enough to withstand the centrifugal forces generated at these speeds. The very thin, highly polished aluminum overcoat protected by a vapor deposit quartz coating creates a reflective surface that is both efficient and very durable.
Light enters the camera through objective and field lenses and is reflected by the spinning mirror. These cameras produce streak images by reflecting the thin line of light from the slit directly to the film track. Frame records are produced by a method described as the Miller Principle for shuttering and image transmission. A bank of relay lenses and shuttering stops arranged in an arc coaxial with the film track receives light swept by the rotating mirror. As the light enters successive shuttering stops and associated lenses, an image is relayed to the film.
Rotating mirror cameras produce frame records at up to 25 million frames per second, and streak records at up to 30 mm per microsecond with resolution that often exceeds the limits of the film.

ROATING MIRROR CAMERA