LESSON 04
The exposure triangle
Aperture, shutter speed and ISO all change brightness. Each one also changes something else, and that is how you choose.
THREE CONTROLS · ONE BRIGHTNESS
- ApertureDEPTH OF FIELD
- Shutter speedMOTION BLUR
- ISONOISE
A triangle: aperture at the top, shutter speed and ISO at the base corners; each corner also controls depth of field, motion blur or noise.
Three controls, one exposure
Exposure is decided by how long the shutter stays open, how wide the lens opens and how bright the scene is. ISO then sets how brightly that exposure is read. Change any one of them by a stop and the picture is twice or half as bright.
Trading stops
Take a stop from one corner and give it to another, and the brightness stays the same. Each line below is the same exposure: two stops less aperture paid for by two stops more time, or by two stops more ISO.
| Aperture | Shutter | ISO |
|---|---|---|
| f/2.8 | 1/500 s | ISO 100 |
| f/5.6 | 1/125 s | ISO 100 |
| f/5.6 | 1/500 s | ISO 400 |
Same brightness, different picture
Equal exposures do not make equal pictures. The wide-open frame has the softest background, the fastest shutter freezes the most motion, and the highest ISO shows the most noise.
Choose the corner that matters
Decide first what this picture needs: a soft background, frozen motion or the cleanest file. Fix that setting, set the second one for the light, and let the third make up the difference.
Try it today
- 01Set M and find a correct exposure on a still subject.
- 02Open the aperture one stop and make the shutter one stop faster.
- 03Shoot, then repeat twice more.
- 04Now raise ISO one stop and close the aperture one stop.
- 05Line the frames up: same brightness, different pictures.
Figures from Wikipedia, 'Exposure (photography)' and 'Exposure value', read 2026.10.16. The three equal exposures are worked out from the one-stop steps the article describes. The steps under Try it today are working practice, not a standard.