ISO 2721:2013

ISO 2721:2013 specifies the exposure at the focal plane of film-based cameras for values of two exposure parameters, i.e. field luminance and film speed, and also describes methods of evaluating other photometric characteristics, such as the acceptance angles of the photoelectric system.
ISO 2721:2013 applies to automatic exposure control systems which are built into film-based cameras or coupled with them to regulate the exposure in the focal plane as a function of the several exposure parameters.