Mastering the exposure triangle: everything you need to know

What is aperture?

The aperture is the opening inside your camera’s lens that lets light through to the sensor. It can vary in size to let in more or less light, thereby brightening or darkening your image. 

Controlling aperture also lets you determine how much of your image is in focus. Very wide apertures let in a lot of light, but only a sliver of what you see will be in focus. Smaller apertures provide more focus through a deeper focal plane, but don’t let as much light through. Neither is better or worse than the other. It’s about knowing which to use for the situation and aperture is also a creative choice. A portrait in which the face is in focus but the background and foreground are blurred can look great, while a vast landscape where everything is in focus from back to front can also be wonderful.

Aperture settings are measured in called f-stops, f-numbers. An example would be f/1.2. The lower the number, the wider the opening, so f/1.2 is quite wide. Higher numbers, such as f/16 or f/22, denote smaller apertures. 

Read more: What is aperture?

What is shutter speed?

Your shutter is the part inside your camera that opens and closes to let light through to the sensor, like shutters on a window. Light hits it after coming through the aperture in your lens. Opening the shutter lets light through to the camera’s sensor. Shutter speed refers to how fast it will open and close and is measured in fractions of a second or in whole seconds.

Slower shutter speeds (such as 1/15 sec) can cause moving subjects to appear blurred, while faster shutter speeds can freeze motion. A high shutter speed of 1/1000 sec, for example, is commonly used to freeze fast-moving subjects such as wildlife. Faster shutter speeds can also darken your photo, because they only let light through for a small fraction of a second, giving it less time to register on your camera’s sensor. 

What is ISO?

ISO refers to how your sensor reads light, specifically its sensitivity to light. Lower ISO numbers, such as 100, denote a low sensitivity to light. Higher ones, for example, 1600, boost light sensitivity.

Higher ISO settings can produce digital grain in your photos called ‘noise’, though modern cameras have improved noise reduction. For that reason, lower ISO settings are often recommended whenever possible. 

How do aperture, shutter speed and ISO interact?

Changing one setting almost always means changing others to accommodate it. A faster shutter speed, which reduces the amount of light getting in, for example, may require you to boost your ISO or open your aperture wider for a bright enough image. How your settings balance each other will depend on the image you’re trying to create. 

Which element of the exposure triangle should I prioritise?

Say you’re photographing birds in the wild. You want a shot that freezes one in flight with no blur. You’ll need a fast shutter speed, but also a small enough aperture to get the whole bird in sharp focus. Both will darken your image, so how would you get a well-exposed photograph that meets your goal? 

What is the most essential setting for the image?

One way to figure this out is to work backwards from your most important setting. In this situation, that’s shutter speed because you need to freeze motion. Say you need a speed of 1/2000 sec. How can you get a brighter exposure using your other settings? You could: 

• Open your aperture wider
• Boost your ISO

Look at your second most important setting after shutter speed: an aperture that gets everything in focus. Since you want to be sure your image is sharp, you’ll want to avoid wider settings such as f/1.4 or f/1.8, because those only get a small slice of your image in focus. You’ll need to choose a setting that’s still relatively wide to let in more light while narrow enough to get the bird in focus, probably f/4 to f/5.6. 

Lastly, look at your ISO. To avoid noise, you’ll want to keep it on the lower side, but don’t be afraid to raise it enough to get a bright, sharp photo. To dial your ISO in, take a few test shots after figuring out your shutter speed and aperture. Once you’ve settled on something that gives you a nice bright exposure, you’re ready to go. 

Can the camera help adjust the exposure parameters?

Absolutely. If it all seems overwhelming to try at once, don’t worry. Focus on one setting at a time by using modes such as aperture priority or shutter priority and build out from there. You can find a full guide to camera modes here. Many professional photographers, especially those working in fast-paced situations, use these modes rather than balancing the exposure in manual mode every time, so you’re in good company.