Exposure Calculator

Starting aperture f/

Starting shutter 1/

Starting ISO

New aperture f/

New ISO

Result

Shutter needed1/31
EV at ISO 1007.94
Stops of aperture2
Stops of ISO0
Net stops to compensate2
Hand-holdingslower than 1/60 — you want a tripod or stabilisation

Three settings, one exposure

Works out the shutter speed that preserves exposure at a different aperture or ISO, and expresses the changes in stops.

Shutter, aperture and ISO are linked so that the same exposure can be reached many ways. Close the aperture two stops and either quadruple the shutter time or quadruple the ISO, and the frame comes out equally bright.

A stop is exactly a factor of two: twice the light or half of it. Aperture is measured by the area of the opening, so its series runs in steps of the square root of two — 1.4, 2, 2.8, 4, 5.6, 8, each one costing a stop.

What this calculator shows

The shutter speed that preserves exposure at the new aperture and ISO
The exposure value normalised to ISO 100
The change in stops on aperture and on sensitivity

What to keep in mind

The arithmetic is purely geometric: real lenses lose light to their coatings, which is why T-stops differ from f-numbers.
Hand-holding without stabilisation works to about 1/60 of a second, or to the reciprocal of the equivalent focal length.

FAQs

What is a stop of exposure?

A change of exactly a factor of two in light. One stop is a doubled shutter time, the next value in the aperture series, or a doubled ISO.

Why is the aperture series so odd?

Because light depends on the area of the opening, not its diameter. To halve the area the diameter changes by the square root of two — hence 1.4, 2, 2.8, 4.

What does EV mean?

Exposure value: a shutter and aperture pairing normalised to ISO 100. EV 15 is roughly bright sunshine; EV 0 is dusk.

Which setting should I change first?

It depends on the shot. Aperture controls depth of field, shutter controls motion blur, ISO controls noise. Move whichever matters least in this frame.

Worked example

Closing down two stops

Input: f/2.8 at 1/125 and ISO 400 → f/5.6 at the same ISO

Output: Shutter 1/31, EV at ISO 100 is 7.94

Note: Two stops of aperture means four times the shutter time. Hand-holding at 1/31 is a stretch: either raise the ISO or find something to rest the camera on.

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Exposure Calculator

Result

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