From AMS Glossary
A camera used for the observation of lightning flashes.
The early model of this camera consists of a fixed film plate and two lenses that revolve at the opposite ends of a diameter of a circle. The velocity and duration of a lightning stroke can be computed from a comparison of the two photographs and a knowledge of the rate of rotation of the lenses. A later model consists of a fixed lens and a rotating film drum. This construction allows greater ease of interpretation.