Why is the speed rating of motion picture camera films given in Exposure Indices rather than ASA or DIN values?
There is no ANSI standard to determine the speed of these films. The speed of motion picture camera films and the suggested filtrations are determined on the basis of practical picture tests. Suitable safety factors have been included to allow for differences in cameras, variation in lighting, etc. The exposure index values should not be regarded as numbers which express the absolute speed or sensitivity of the film, neither should they be regarded as fixed values which can not be changed if the results of repeated tests indicate the need for such changes.
