Mastering Light: Exposure Value (EV)
Exposure Value (EV) is a base-2 logarithmic scale that represents all combinations of a camera's shutter speed and aperture that result in the same level of exposure. The concept was developed in the 1950s to simplify the relationship between camera settings and the brightness of the scene being photographed.
The EV Scale
- EV 0: Corresponds to an exposure of 1 second at f/1.0 (at ISO 100).
- EV 15: Typical 'Sunny 16' light (bright daylight).
- EV -6: Extreme low light, such as a moonless night in the wilderness.
Reciprocity and EV
The beauty of the EV system is Reciprocity. If a scene has an EV of 12, you can use any combination of settings that equals 12:
- 1/125s at f/8
- 1/250s at f/5.6
- 1/500s at f/4 All three settings will result in the exact same amount of light hitting the sensor.
The Formula
EV = log₂(N² / t)
Where:
N=
Aperture (f-number)t=
Shutter speed in seconds(Note: This standard formula assumes ISO 100. For other ISOs, the EV is shifted accordingly.)