Exposure Value (EV) Converter

What the exposure value converter does

The exposure value converter links the four quantities that define a photographic exposure: aperture, shutter speed, ISO and exposure value (EV). Enter aperture, shutter speed and ISO to find the EV of the settings you are using, or enter an EV, ISO and shutter speed to find the aperture that matches it. Press Calculate and the result appears with the working shown.

The formula

EV = log₂(N² / t) − log₂(ISO / 100)

N is the f-number and t the shutter time in seconds. The first term is the classic EV at ISO 100; the second corrects for sensitivity. When you supply an EV instead, the tool keeps your shutter speed and ISO and solves for the aperture: N = √(t × 2^{EV + log₂(ISO/100)}).

Worked examples

The default values give EV 9.6: log₂(2.8² ÷ 0.01) = log₂(784) = 9.6 at ISO 100.

Equivalent exposures

Every combination with the same EV lets the same amount of light reach the sensor. EV 12 at ISO 100 is f/16 at 1/15 s, f/8 at 1/60 s, f/4 at 1/250 s and f/2 at 1/1000 s. The photographer picks among them for depth of field and motion: the f/16 version keeps everything sharp but needs a tripod; the f/2 version freezes motion and isolates the subject. Raising ISO shifts the whole set: at ISO 400 the same scene is f/8 at 1/250 s.

The stop scale

Aperture steps are multiples of √2 because light gathered depends on the area of the opening, which goes with the square of the diameter. Cameras add ⅓-stop positions between the full stops (f/8, 9, 10, 11).

Using EV in practice

• Manual exposure without a meter. Estimate EV from the scene, then use the converter to find settings at your ISO.
• Checking a meter reading. Hand-held meters display EV; the converter turns that into an aperture at the shutter speed you want.
• Exposure compensation. Adding +1 EV in camera means the camera targets one stop more exposure than its meter suggests.
• Comparing cameras. A lens rated for autofocus down to EV −3 works in far dimmer light than one rated to EV 0.
• Neutral density filters. A 6-stop ND lowers the scene’s effective EV by 6, allowing long exposures in daylight.

Common mistakes

• Entering 1/250 as 250. Shutter time is in seconds: 0.004.
• Reading EV as brightness at any ISO. Scene EV tables assume ISO 100; the converter’s ISO term makes the adjustment.
• Confusing EV with exposure compensation. The first is an absolute light level; the second is an offset from the meter.
• Using T-stops as f-stops. Cinema lenses are marked in T-stops, which include transmission loss and give slightly darker results than the f-number suggests.

Related tools

The aperture to exposure converter solves for shutter speed or aperture from a known EV, and the shutter speed converter turns fractions into decimal seconds. Since EV is a base-2 logarithm, the logarithm calculator and exponential form converter help when working the formula by hand.

External references

• Wikipedia: Exposure value
• ISO 2720: general purpose photographic exposure meters

Frequently asked questions

What does one EV mean?

One stop: a factor of two in light. EV 10 admits twice as much light as EV 11 for the same scene brightness.

Why does higher ISO give a lower EV in the calculator?

The formula reports the EV that the aperture and shutter alone would need at ISO 100. A higher ISO means the same scene can be shot with settings that pass less light, so the reported EV falls.

Is EV the same as lux?

They are related but not identical. Roughly, illuminance in lux ≈ 2.5 × 2^EV for incident light at ISO 100, so EV 15 is about 82,000 lux.

Can EV be negative?

Yes. EV 0 is f/1 at 1 s at ISO 100. Moonlight and starlight scenes range from about −2 to −6.

How precise should I be?

Within a third of a stop. Meters, lenses and sensors all carry tolerances of that order.