Understanding the Exposure Triangle

Every photograph is made of light. The exposure triangle is simply the three settings that decide how much of that light reaches your sensor, and what each choice does to the look of the image.

1. Aperture: how wide the lens opens

Aperture is the opening inside your lens, measured in f-stops such as f/1.8, f/4 or f/11. The numbering feels backwards at first: a smaller number means a wider opening and more light.

Aperture also controls depth of field, how much of the scene looks sharp. A wide aperture like f/1.8 gives a shallow depth of field, with the soft, blurred background that portraits love. A narrow aperture like f/11 keeps more of the scene in focus, which suits landscapes and group photos.

2. Shutter speed: how long the light comes in

Shutter speed is how long the shutter stays open, written in fractions of a second such as 1/1000, 1/125 or 1/30. Faster speeds let in less light and freeze motion. Slower speeds let in more light and show motion as blur.

A useful starting rule for handheld shooting: keep your shutter speed at least as fast as one over your focal length. On a 50mm lens, aim for 1/50 or faster to avoid blur from your own hands. Moving subjects such as children or dancers usually need 1/250 or faster.

3. ISO: how sensitive the sensor is

ISO sets how strongly the camera amplifies the light it receives. Low values such as ISO 100 give the cleanest image. Raising ISO brightens the exposure in dim light, but adds noise, a grainy texture that grows as the number climbs.

How the three work together

The three settings are a balance. Change one and you need to compensate with another to keep the same brightness. Each full step, or "stop", doubles or halves the light:

• Open the aperture from f/4 to f/2.8 (one stop more light) and you can make your shutter one stop faster, from 1/125 to 1/250.
• Lower ISO from 800 to 400 (one stop less light) and you need one stop back from somewhere else: a wider aperture or a slower shutter.

Choose the setting that matters most for your idea first, then let the other two follow.

A simple way to practise

For a portrait, start with the look: choose a wide aperture for a soft background. Then set a shutter speed fast enough to stay sharp. Finally, raise ISO only as far as you need to reach a good exposure. Repeat the exercise for a moving subject, this time choosing shutter speed first. Within a few sessions the triangle stops feeling technical and starts feeling creative.

Keep it on your phone: download my free Triangle Exposure guide on Gumroad.