exposurevalue

Exposure value (EV) is a unit used in photography to express a set of shutter speed, aperture, and ISO combinations that yield the same exposure on the image sensor. It provides a convenient, logarithmic scale for comparing or selecting exposure settings.

At ISO 100, EV is defined by the formula EV = log2(N^2 / t), where N is the f-number (aperture) and t is the exposure time in seconds. This means that different pairs of aperture and shutter speed can produce the same EV and therefore the same exposure. For example, at ISO 100, an exposure of about f/2.8 at 1/500 s is roughly EV 12, while f/4 at 1/250 s is also near EV 12. The exact value depends on the precise sensor response and measurement, but the concept is that EV encodes exposure level independent of a specific combination.

Usage and interpretation: EV is widely used in light metering and exposure planning. Many cameras report EV (often as EV stops) to indicate how bright the scene is relative to a reference exposure. Exposure compensation adjusts the camera’s selected EV by adding or subtracting stops (e.g., +1 EV doubles the exposure, -1 EV halves it), allowing the photographer to deliberately brighten or darken a scene.

Limitations and notes: EV is defined relative to ISO 100, and real-world brightness interacts with ISO, sensor characteristics, and processing. When ISO is changed, equivalent exposure settings shift in stops, and some meters report EV adjusted for the current ISO. EV stops provide a convenient framework for manual exposure design and for communicating exposure decisions.