Exposure Triangle Explained
Three controls, one result: the amount of light that reaches your sensor. Here's what each one does, how they trade off, and which to change first — with numbers you can verify in the exposure equivalence calculator.
The three corners
| Control | What it changes | Cost of overdoing it | One stop = |
|---|---|---|---|
| Aperture (f/) | Amount of light + depth of field | Narrow apertures → diffraction softness | f/2.8 → f/4 → f/5.6 → f/8… (each halves the light) |
| Shutter speed (s) | Amount of light + motion blur | Slow speeds → camera shake and subject blur | 1/500 → 1/250 → 1/125 → 1/60… (each doubles the light) |
| ISO | Amplification of the captured light | High ISO → visible noise | 100 → 200 → 400 → 800 (each doubles sensitivity) |
The trade-off, with real numbers
Say your meter says f/4 · 1/250 s · ISO 100. That's an exposure value of EV100 = 12. Every combination below captures the same amount of light:
| Aperture | Shutter | ISO | Result |
|---|---|---|---|
| f/4 | 1/250 s | 100 | Starting point — balanced |
| f/2.8 | 1/500 s | 100 | Shallower DoF, freezes motion |
| f/5.6 | 1/125 s | 100 | More DoF, risk of blur |
| f/4 | 1/500 s | 200 | Faster shutter, ISO doubles |
| f/8 | 1/60 s | 100 | Maximum DoF, needs steady camera |
Every row is identically bright. The only differences are aesthetic: depth of field, motion blur, and noise. That's why "correct exposure" is a creative choice, not a number.
Which corner to change first (priority order)
- Shutter speed first — set the slowest speed that still freezes your subject (1/focal length handheld, or the subject chart). Motion blur is the one mistake you can't fix.
- Aperture second — dial the depth of field your shot needs (f/1.8 portrait vs f/8 landscape), then…
- ISO last — raise ISO only to make up the remaining difference. Modern cameras are clean up to ISO 1600–3200; noise beats blur.
Common exposure mistakes
- "I'll fix it in post." Raising exposure in editing amplifies noise and clips highlights. Better to expose right (or deliberately overexpose by ⅓–⅔ stop for shadows, then recover — the "expose to the right" technique).
- Chasing shallow DoF everywhere. f/1.2 portraits with drifting focus are soft; the portrait guide shows when to stop down.
- ISO fear. On a modern camera, ISO 3200 in low light is usually better than a 1/15 s blurry shot at ISO 100.
Related tools & guides
Exposure Equivalence Calculator
Generate every equivalent exposure for your settings.
Open →Shutter Speed Chart
The right shutter for every subject.
Read →Depth of Field Calculator
See exactly what your aperture choice does.
Open →Exposure triangle FAQ
Does ISO really belong in the "exposure" triangle?
Strictly, exposure is light only (aperture × shutter). ISO is amplification applied after capture. But in practice the three work together to set final brightness, so the triangle is the useful mental model — with the caveat that ISO doesn't add light, it adds noise.
What is "stopping down" and "opening up"?
One stop = doubling or halving the light. Opening up (wider aperture, slower shutter, higher ISO) doubles light; stopping down halves it. The exposure equivalence calculator does the bookkeeping for you.
Why do my photos look different at the same exposure?
Because exposure isn't the whole picture — the character changes with settings: bokeh from aperture, blur from shutter, grain from ISO. Same brightness, different image. That's exactly why the triangle matters.