The exposure triangle explained: aperture, shutter and ISO

The short version: The exposure triangle describes how aperture, shutter speed and ISO work together to control image brightness. Aperture also affects depth of field, shutter speed affects motion blur, and ISO helps you balance the other two. Start with the setting that matters most to your photograph, then adjust the others around it.

What the three settings control

Aperture is the opening in the lens. A lower f-number, such as f/2.8, means a wider opening than f/8. With other conditions unchanged, it lets more light reach the sensor and gives a shallower depth of field.

Shutter speed is the exposure time. A short exposure, such as 1/1000s, helps freeze movement. A longer one, such as 1/15s, records more light but gives movement more time to blur.

ISO affects how bright the recorded image is rendered and how the camera meters exposure. It does not increase the amount of light arriving at the sensor when aperture and shutter speed stay fixed.

Nikon’s exposure triangle guide covers the relationship and creative trade-offs. The triangle is a useful way to organise decisions; it does not mean all three settings physically collect light.

How exposure stops work

A stop is a doubling or halving. Nikon’s exposure guide explains how this connects the settings.

These changes each brighten the picture by roughly one stop when everything else stays the same:

Aperture from f/4 to f/2.8.
Shutter speed from 1/250s to 1/125s.
ISO from 400 to 800.

Reverse any of them and the picture becomes one stop darker. Many cameras adjust in thirds of a stop, so three dial clicks often make a full stop.

You do not need to memorise every value. Learn a few neighbouring settings and watch the exposure scale while you practise.

Different settings can give similar brightness

Suppose f/4, 1/250s and ISO 400 give the brightness you want. In unchanged light, these alternatives should look similarly bright:

f/2.8, 1/500s, ISO 400: a wider aperture balances the shorter exposure.
f/4, 1/500s, ISO 800: a higher ISO balances the shorter exposure.
f/5.6, 1/125s, ISO 400: a longer exposure balances the smaller aperture.

They will not necessarily look like the same photograph. Depth of field, motion blur and noise can change.

These are worked examples using the usual rounded camera settings. They explain the trade, rather than prescribe settings for a particular room or time of day.

Choose the most important setting first

For a running dog, start with motion. Try 1/1000s, inspect the result and go faster if needed. Then choose an aperture that gives enough depth of field and let ISO take up the remaining adjustment.

For a group portrait, start with depth of field. Arrange faces at similar distances and try f/5.6 or f/8. Keep shutter speed high enough for people shifting about.

For a waterfall with flowing blur, start with a longer shutter speed and support the camera. In bright conditions, even a low ISO and small aperture may leave too much light; a suitable neutral density filter is one way to reduce it.

These choices follow the photograph you want to make. There is no single balanced triangle setting.

Let automatic modes do some of the work

Aperture priority lets you choose aperture while the camera sets shutter speed. Shutter priority reverses those roles. Auto ISO can add another automatic adjustment.

Watch the settings the camera chooses. Aperture priority is useful for controlling depth of field, but it can select a shutter speed that is too slow for your subject.

The meter is a starting point. If an automatic exposure looks too dark or too bright, use exposure compensation and check again. Fully manual exposure with fixed ISO normally needs a direct settings change instead.

Try this

Find a scene with steady light and use manual mode with a fixed ISO. Make one photograph at f/4 and 1/250s, adjusting ISO first if necessary.

Change to f/2.8 and 1/500s for the next frame. Compare brightness and background detail. Then return to f/4, keep 1/500s and double ISO.

Read the settings beside each photograph during playback. Keep practising with paired changes until you can predict the result before pressing the shutter.