Exposure Value (EV)

Exposure Value (EV): a single number for light

The Exposure Value rolls aperture and shutter speed into one scale: EV = log₂(N²/t), where N is the f-number and t is the shutter time in seconds. Going up +1 EV halves the light hitting the sensor; dropping −1 EV doubles it. A few reference points at ISO 100: EV 15 is Sunny 16 (bright daylight), EV 12 overcast, EV 8 a bright interior, EV 3 a candle-lit room, EV −1 a close-up of one candle, and EV −6 a landscape under stars. When the histogram sits balanced, with nothing clipped at either end, it usually lines up with the metered EV. Reach for exposure compensation (±EV) on bright scenes (snow +1) or dark ones (black cat −1). Lightroom's "Exposure" slider runs in EV stops, and HDR brackets usually grab 3–5 frames at ±1 or ±2 EV intervals.

Applications

You'll use it to measure available light, keep exposure consistent as scenes shift, put scenes side by side on a common scale, build HDR sequences through bracketing, and dial in Lightroom/Capture One sliders in known stops. It's hard to do without on manual cameras or fixed-exposure setups.

FAQ

Does EV depend on ISO? The bare formula doesn't. But once you map EV to the actual exposure on the sensor, ISO comes in too, since doubling it amounts to +1 EV of sensitivity.

What is "EV 0"? It's 1 second at f/1.0, the original reference point set back in the 1950s.

Why bracket ±2 EV instead of ±1 EV? A high-contrast scene like a sunrise, or an interior shot toward windows, can span 10+ stops. Wider brackets pull in the shadows and the highlights so you have both to merge.