A film cassette comprises a film spool supported inside a lighttight shell for rotation to thrust a filmstrip coiled about the spool automatically to the exterior of the shell, and a film exposure status indicator supported for rotation relative to the shell from an unexposed position for providing a...http://www.google.es/patents/US5032861?utm_source=gb-gplus-sharePatente US5032861 - Film cassette with lock-out means for preventing load of exposed film
Film cassette with lock-out means for preventing load of exposed film
