Douglas A. Kerr. APEX-The Additive System of Photographic Exposure

The Additive System of Photographic Exposure (APEX) provides for stating several factors involved in photographic exposure in logarithmic form. In this way, calculation of the proper exposure for a given situation may be done manually using only addition. Although the importance of that has largely faded since the time the system was developed, the scheme is still widely used in technical work relating to photographic exposure, especially the quantity exposure value (E V ). This article explains the APEX system, and gives cautions about irregularities in its usage that are often encountered.