Enter shutter speed as a fraction such as 1/250, or as whole or decimal seconds such as 2 or 0.5.
Change one side of the triangle by a number of stops, then pick a second side to compensate with and keep the same overall exposure.
| Stops | ISO | Aperture | Shutter speed |
|---|
What exposure value actually measures
Exposure value combines aperture and shutter speed into a single number that describes how much light reaches the sensor, independent of ISO. The reference figure, EV at ISO 100, is calculated as the base-2 logarithm of the aperture squared divided by the shutter time in seconds, so a wider aperture or a slower shutter both push the number down while a smaller aperture or a faster shutter push it up.
Why ISO shifts the picture
Raising ISO does not change how much light physically hits the sensor, it changes how that light is amplified, which is why the calculator shows a second figure adjusted for your chosen ISO. Doubling ISO from 100 to 200 lowers the exposure value needed by one stop, because the sensor now needs half as much light to produce the same brightness.
Trading one side of the triangle for another
Any two combinations of ISO, aperture, and shutter speed that produce the same exposure value will look equally bright, even though the aperture affects depth of field and the shutter speed affects motion blur very differently. The equivalent exposure section holds one parameter fixed and works out how far the other one has to move, in stops, to cancel out a change you made elsewhere in the triangle.
Full, half, and third stops
A full stop always doubles or halves the amount of light. Shutter speed and ISO scale directly with that doubling, but aperture is based on the diameter of the opening rather than its area, so a full stop in f-number is a multiple of the square root of two rather than two itself. Half and third stops split that same doubling into smaller, evenly spaced steps, which is how most cameras let you fine-tune exposure beyond the traditional full-stop markings.