Exposure Triangle Calculator
Equivalent exposure settings when you change aperture or ISO.
Results
- Equivalent shutter speed
- 1/2000
- Nearest setting on your camera
- 1/2000
- Shutter change
- -4.0 stops
The shutter speed that gives the same overall exposure as your reference settings, at the new aperture and ISO.
The closest speed on the standard third-stop dial, since cameras can't be set to arbitrary fractions.
How far the shutter has to move to absorb your aperture and ISO changes. Positive means a longer exposure, negative means a shorter one.
How it works
Aperture, shutter speed and ISO all trade against each other in stops, where one stop means a doubling or halving of the light reaching the sensor. Give up a stop of aperture and you can take it back with a stop of shutter speed or a stop of ISO, and the brightness of the final image stays put.
What changes is everything else. Aperture controls depth of field, shutter speed controls how motion renders, and ISO controls noise. The triangle is a way of choosing which of those three you care about most in a given shot and letting the other two absorb the consequences.
Aperture is the one that trips people up, because light scales with the square of the f-number rather than linearly. Going from f/2.8 to f/4 is one stop, not the 1.4 the numbers suggest, which is why the standard aperture sequence looks so arbitrary until you notice each step is the previous one times the square root of two.
The formula
t₂ = t₁ × (N₂ / N₁)² × (ISO₁ / ISO₂)
t is shutter time, N the f-number, and subscripts 1 and 2 the reference and new settings. The aperture term is squared because light scales with the area of the opening.
Frequently asked questions
- Why isn't f/4 twice as much light as f/2?
- Because the f-number describes a diameter while light depends on area. Doubling the diameter quadruples the area, so f/2 to f/4 is two stops, not one.
- Why can't I set the exact speed shown?
- Cameras only offer a fixed ladder of speeds, usually in third-stop steps. The nearest setting shown is the closest real value on that ladder; the small residual difference is far below what you would notice.
- Does this account for reciprocity failure?
- No. Digital sensors respond linearly, so the calculation holds throughout. Film loses sensitivity during very long exposures and needs extra time beyond what this predicts, by an amount specific to each stock.