The Photography Exposure Triangle Explained

If you're just getting started with photography, you've probably heard the term "exposure triangle." It's the foundation of how cameras work—and it's not as complicated as it sounds.

The exposure triangle is made up of three settings that control how bright or dark your photo will be:

• Aperture – how wide your lens opens
• Shutter Speed – how long your camera's sensor (or film) is exposed to light
• ISO – how sensitive your sensor or film is to light

All three are connected. Change one, and it affects the others. That's why it's called a triangle—there's a balance involved.

Understanding the exposure triangle helps you take control of your photos, rather than leaving everything up to auto mode. It lets you:

• Choose whether your photo is sharp or has motion blur
• Control how much of your scene is in focus (depth of field)
• Get the right brightness without sacrificing image quality

Once you understand how these three settings interact, you can use them creatively instead of just technically.

Aperture refers to how wide the lens opens when taking a photo. It's measured in f-stops like f/2.8, f/5.6, or f/11.

A wider aperture (like f/1.8 or f/2.8) lets in more light and gives you a shallower depth of field, meaning only part of the image is in focus. This is great for portraits where you want a blurry background.

A narrower aperture (like f/8 or f/16) lets in less light but gives you more depth of field, so more of the image appears sharp—useful for landscapes or product photography.

Shutter speed controls how long your camera's sensor or film is exposed to light. It's measured in seconds or fractions of a second—like 1/1000 (very fast) or 1/30 (slower).

A fast shutter speed (like 1/1000) freezes motion—great for sports, wildlife, or fast-moving subjects.

A slower shutter speed (like 1/10 or 1 second) lets in more light but can create motion blur. You might use this for artistic shots, low-light scenes, or to capture movement like waterfalls or car trails.

ISO measures how sensitive your sensor (or film) is to light. Lower numbers like ISO 100 or 200 are less sensitive, while higher numbers like ISO 1600 or 3200 are more sensitive.

Use low ISO when there's plenty of light—your images will be cleaner with less grain or noise.

Use higher ISO in darker settings when you need to brighten things up—but expect some added grain, especially with digital sensors.

With film, ISO is set by the roll you're using (like ISO 400 film), so you'll want to meter your light based on that fixed number.

Each side of the triangle changes how your photo looks—and feels.

The real skill comes in balancing the three settings based on the lighting and what kind of image you want to create. Here's a quick example:

Let's say you're shooting a portrait in natural light, but it's starting to get dark. You might:

• Open your aperture to f/2.8 to let in more light
• Lower your shutter speed a bit, but not too much or you'll get blur
• Raise your ISO slightly to brighten the image without too much noise

There's no one perfect setting—it's all about tradeoffs. The more you practice, the more intuitive it becomes.

Learning the exposure triangle is one of the biggest steps in becoming a confident photographer. It takes a bit of trial and error at first, but once it clicks, you'll be able to look at a scene and know exactly how to expose it.

You'll start to see light differently. You'll think about your photos more intentionally. And you'll have way more creative control over the final image.

If you're learning manual photography or shooting film, Thea makes understanding the exposure triangle much easier. It's a free light metering app for iPhone that shows you real-time exposure readings based on your current settings.

You can choose between aperture priority, shutter priority, or manual mode—depending on which part of the triangle you want to control. Thea shows you the matching settings that complete the triangle for a correct exposure.

You can also limit your aperture, shutter speed, or ISO to match your camera or film, which is especially helpful when you're learning how different settings interact.

The best part? You can try things out without even picking up your camera. Use Thea to meter a scene, adjust settings, and see how the exposure changes. It's a hands-on way to understand the triangle—without wasting a roll of film or guessing your settings.