What is the Exposure Triangle?
The exposure triangle is the foundation of photography. It describes how three camera settings — aperture, shutter speed, and ISO — work together to control how much light reaches your sensor, and therefore how bright or dark your photo turns out. The catch: each setting has a creative side effect beyond just brightness.
Aperture
Aperture is the size of the lens opening, expressed as an f-number (f/1.4, f/5.6, f/16). A wide aperture (low f-number) admits more light and produces a shallow depth of field — ideal for portraits where you want the background to blur. A narrow aperture (high f-number) admits less light but keeps the entire scene sharp, which is what landscape photographers want.
Shutter Speed
Shutter speed controls how long the sensor is exposed to light. A fast shutter (1/1000s or faster) freezes motion — great for sports and wildlife — but lets in less light. A slow shutter (1/30s or slower) lets in more light but will blur anything that moves. Slow shutters are used intentionally for silky waterfalls and light trails.
ISO
ISO controls how sensitive your sensor is to light. Low ISO (100–400) produces clean, sharp images and should be your default. High ISO (1600–6400) brightens dark scenes but introduces digital noise — a grainy texture that degrades image quality. Raise ISO only when aperture and shutter speed can't get you to a correct exposure.
Balancing the Triangle
A correct exposure happens when all three settings are in balance for the light in your scene. The key insight is that each stop of change is equivalent across all three controls. Open your aperture one stop, or slow your shutter one stop, or double your ISO — each adds exactly the same amount of light. This means you can freely trade one setting for another without changing the overall exposure, while consciously choosing the creative trade-offs that come with each.