Off-the-film metering in a photographic film camera is improved by measuring actual film reflectivity at the time of film manufacture and recording a film adjusted exposure constant on a magnetic recording layer on the film. Camera apparatus is provided to read this film adjusted exposure constant value...http://www.google.de/patents/US5184174?utm_source=gb-gplus-sharePatent US5184174 - Photographic system with off-the-film exposure metering
