Exposure Value (EV)
Combines aperture and shutter speed into one exposure figure.
Formula
Variables
Example
f/4, 1/60 s: EV = log2(16×60) ≈ 9.9
How it works
Exposure value (EV) is a compact way to describe how much light a camera setting lets in by combining aperture and shutter speed into one number. The aperture term uses N^2 because a lens opening gathers light in proportion to its area, and the area of a circular opening depends on the square of the f-number. The logarithm base 2 is used because each increase of 1 EV represents a halving of the light reaching the sensor, so the scale matches common photographic adjustments.
When to use it
Use this when you want to compare different camera settings that give the same brightness, such as choosing between a wider aperture and a faster shutter. It is also useful for understanding exposure charts, camera metering, and how much you need to change settings when lighting conditions change.
Worked example, step by step
Given N = 5.6 and t = 1/125 s Step 1: Square the f-number: N^2 = 5.6^2 = 31.36 Step 2: Divide by shutter time: N^2 / t = 31.36 / (1/125) = 31.36 × 125 = 3920 Step 3: Take base-2 logarithm: EV = log2(3920) Step 4: Evaluate: EV ≈ 11.94 Final answer: EV ≈ 11.9
Common mistakes to avoid
- Using the aperture number N instead of N^2
- Putting shutter speed in as 125 instead of 1/125 s
- Forgetting that EV changes by 1 for each doubling or halving of light
Did You Know?
EV 0 is defined as f/1.0 at 1 second — every whole EV step up halves the light reaching the sensor.
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