Exposure Value - Camera Settings Vs. Photometric Exposure

Camera Settings Vs. Photometric Exposure

“Exposure value” is somewhat of a misnomer, because it indicates combinations of camera settings rather than the photometric quantity of luminous exposure H_v (aka photometric exposure), which is given by (Ray 2000, 310)

where

• H_v is the photometric / luminous exposure
• E_v is the image-plane illuminance (not EV, the exposure value)
• t is the exposure time

The illuminance E_v is controlled by the f-number but also depends on the scene luminance L_v. To avoid confusion, some authors (Ray 2000, 310) have used camera exposure to refer to combinations of camera settings. The 1964 ASA standard for automatic exposure controls for cameras, ASA PH2.15-1964, took the same approach, and also used the more descriptive term camera exposure settings.

Common practice among photographers is nonetheless to use “exposure” to refer to camera settings as well as to photometric exposure.