A photo's brightness is a team effort: aperture (how wide the eye opens), shutter (how long it stays open), and ISO (how sensitive the sensor is). The exposure triangle is balancing those three dials to let in just the right light.
Three dials, one bright picture
A photo's brightness is set by three linked controls: aperture (how wide the lens opens), shutter speed (how long the sensor is exposed), and ISO (the sensor's sensitivity). Together they form the exposure triangle — change one and you usually adjust another to keep the brightness right.
f/4 · 1/125s — Balanced exposure
A wider aperture (smaller f-number) or slower shutter lets in more light. Each step is one stop — a doubling or halving.
Slide the aperture and shutter and watch the scene brighten or darken. Balance them for a clean exposure.
- Set a balanced exposure in the simulator.
- Open the aperture one step (smaller f-number) — the image brightens.
- Speed up the shutter one step to bring it back to balanced.
What you should see: Each step is one 'stop'. Opening the aperture one stop and shortening the shutter one stop cancel out — the trade at the heart of exposure.