The exposure triangle
The single most useful thing to understand in photography. Pick a scene, drag the three settings, and watch how aperture, shutter speed, and ISO trade off — in brightness and in the look of the shot.
A dim room. Aim for a bright, clean shot with a soft, blurred background.
All three corners control light — that's the triangle. The inner shape leans toward whichever is gathering the most; move one corner and you rebalance with the others to hold the same exposure.
✓ Balanced for this scene — try changing one setting and rescuing the exposure with another.
The lesson: Open the aperture for a soft background — but not so wide you lose an eye to the blur.
The three corners
FAQ
What is the exposure triangle?
It's the relationship between the three settings that control a photo's brightness — aperture, shutter speed, and ISO. Change one and the exposure changes; to keep the same brightness you compensate with another. Each also has a side effect: aperture sets background blur, shutter sets motion blur, and ISO sets noise.
What is a 'stop'?
A stop is a doubling or halving of light. Opening the aperture one stop, slowing the shutter one stop, or doubling the ISO each let in twice as much light. That's why the three trade off cleanly: lose a stop on one, gain it back on another.
How do I keep the same exposure when I change a setting?
Move another setting the opposite way by the same number of stops. Closed the aperture one stop (darker)? Slow the shutter one stop or double the ISO to get the brightness back.
Which setting should I prioritize?
It depends on the shot. For a soft portrait background, start from a wide aperture. To freeze action, start from a fast shutter. In the dark, you'll often have to accept a higher ISO. Set your priority first, then balance the other two for exposure.