Exposure Triangle Calculator

The Exposure Triangle describes the interdependence of three camera settings that together control how much light reaches the sensor and how the image looks.

The three variables:

1. Aperture (f-stop): the size of the lens opening. Larger opening = lower f-number = more light.
2. Shutter Speed: how long the sensor is exposed. Longer = more light; also controls motion blur.
3. ISO: sensor sensitivity. Higher ISO = brighter image; also increases digital noise.

Exposure Value (EV) formula: EV = log₂(f² / t) Where f = f-number and t = shutter speed in seconds.

Relative EV adjustment: ΔEV = log₂(f₁² / f₂²) = 2 × log₂(f₁ / f₂) (for aperture changes) ΔEV = log₂(t₂ / t₁) (for shutter speed changes) ΔEV = log₂(ISO₂ / ISO₁) (for ISO changes)

One stop of light means exactly doubling or halving the exposure:

• Aperture: f/2.8 → f/4 = −1 stop (half the light)
• Shutter: 1/250s → 1/500s = −1 stop
• ISO: 800 → 1600 = +1 stop

Standard full f-stop scale: f/1 · f/1.4 · f/2 · f/2.8 · f/4 · f/5.6 · f/8 · f/11 · f/16 · f/22 · f/32

Each step to a higher f-number halves the light, so the whole scale spans a lot more than it looks: f/1.4 lets in 128 times the light of f/16.

Standard full-stop shutter scale: 1/8000 · 1/4000 · 1/2000 · 1/1000 · 1/500 · 1/250 · 1/125 · 1/60 · 1/30 · 1/15 · 1/8 · 1/4 · 1/2 · 1s

Your camera almost certainly offers third-stops between these, which is why the calculator rounds its answer to a setting the dial actually has and tells you how far off exact that lands.

Worked example: Current settings: f/4, 1/250s, ISO 400. You want to switch to f/8 (depth of field). f/4 → f/8 = −2 stops (4× less light). To compensate: slow shutter from 1/250s → 1/60s (+2 stops), or raise ISO 400 → 1600 (+2 stops), or combine both changes.

Creative trade-offs:

• Wide aperture (f/1.8–f/2.8): blurry background (bokeh): portraits
• Fast shutter (1/1000s+): freeze motion: sports, wildlife
• Low ISO (100–200): maximum image quality: landscapes on a tripod

Which setting you compensate with is the whole decision. Say you are in a dim café at ISO 800, f/2.8, 1/60 and the band starts moving. Push to ISO 3200 and you have two stops to give back: spend them on the shutter and you get 1/250 and the smear is gone; spend them on the aperture and you get f/5.6, a deeper focus, and exactly the same smear you started with. Both hold the exposure. Only one solves the problem.

Common starting points:

The Sunny 16 rule: in full sun, set f/16 and a shutter of roughly 1 over the ISO. At ISO 200 that is 1/200 s. There is some rounding in that: full sun is EV 15, which at ISO 100 and f/16 works out to exactly 1/128, so the honest setting is the 1/125 on your dial rather than the 1/100 the rule implies. A third of a stop is nothing on any film or sensor made in the last fifty years, which is why nobody bothers correcting it.