meter indicates (Ray 2000, 316). For example, an exposure compensation of +1 EV (or +1 step) means to increase exposure, by using either a longer exposure time or a smaller -number. The sense of exposure compensation is opposite that of the EV scale itself. An increase in exposure corresponds to a decrease in EV, so an exposure compensation of +1 EV results in a smaller EV; conversely, an exposure compensation of −1 EV results in a greater EV. Use of APEX values in Exif APEX has seen a partial resurrection in the Exif standard, which calls for storing exposure data using APEX values. There are some minor differences from the original APEX in both terminology and values. The implied value (1/3.125) for the speed scaling constant given in the Exif 2.2 specification ("Exif 2.2"; JEITA 2002) differs slightly from the APEX value of (0.2973); with the Exif value, an ISO arithmetic film speed of 100 corresponds exactly to a speed value of 5. The relationship between and luminance depends on both the speed scaling constant and the reflected-light meter calibration constant : Because Exif 2.2 records ISO arithmetic speed rather than film sensitivity, the value of affects the recorded value of but not the recorded film speed. Exif 2.2 does not recommend a range of values for , presumably leaving the choice to the equipment manufacturer. The example data in Annex C of Exif 2.2 give 1 footlambert for = 0. This is in agreement with the APEX value for , but would imply , or 3.125 with in footlamberts. With in cd/m2, this becomes 10.7, which is slightly less than the value of 12.5 recommended by ISO 2720:1974 and currently used by many manufacturers. The difference possibly arises from rounding in the example table; it also is possible that the example data simply were copied from an old ASA or ANSI standard. Notes References Adams, Ansel. 1981. The Negative. Boston: New York Graphic Society. ANSI PH2.7-1973. American National Standard Photographic Exposure Guide. New York: American National Standards Institute. Superseded by ANSI PH2.7-1986. ANSI PH2.7-1986. American National Standard for Photography — Photographic Exposure Guide. New York: American National Standards Institute. ANSI PH3.49-1971. American National Standard for general-purpose photographic exposure meters (photoelectric type). New York: American National Standards Institute. After several revisions, this standard was withdrawn in favor of ISO 2720:1974. ASA PH2.5-1960. American Standard Method for Determining Speed of photographic