ISO 2721:1982 defines the exposure at the focal plane of cameras for values of two exposure parameters, i.e. field luminance and film speed. It also gives methods of evaluating other photometric characteristics. The data apply to automatic exposure control systems which are built into cameras or coupled with them to regulate the exposure in the focal plane in dependence of the various exposure parameters.
ISO 2721:1982 is applicable to film-based cameras and it is not applicable to digital cameras.