What Is the Exposure Triangle?

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What Is the Exposure Triangle?

Let’s start with something really simple.
Taking a photograph is filling a box with light.
That’s it. No magic. No complicated photography voodoo. We’re trying to get the right amount of light into the camera to create the photograph we want.

Think about filling a glass with water from your kitchen faucet. You have three basic ways to control what happens. You can control how much water comes out of the faucet. You can control how long you leave the faucet running. And you can decide how much water you need in the glass.

Photography works in much the same way. Instead of water, we’re dealing with light. And instead of three parts of a faucet and a glass, we have:

• Aperture
• Shutter Speed
• ISO

Together, these are commonly called the Exposure Triangle.

Aperture

Aperture controls how much light can pass through the lens at one time. Think of it as the size of the opening. A bigger opening lets in more light. A smaller opening lets in less light.

But there’s a catch. Changing the aperture also changes Depth of Field, or how much of the photograph appears sharply focused. So aperture isn’t just about light. It’s also a creative decision. Do I want a shallow area of focus? Or do I want more of the scene to be sharp? We’ll spend a lot more time on that in the aperture lessons.

Shutter Speed

Shutter speed controls how long we allow light into the camera. The shutter opens. Light comes through the aperture. The shutter closes. Done.
Leave it open longer and you get more light. Leave it open for less time and you get less light. Simple.

But there’s another catch. While that shutter is open, things can move. That movement can be recorded as motion blur. Or, with a fast enough shutter speed, you can freeze that movement. This is where shutter speed becomes a very powerful creative tool.

Do I want the water to look soft and dreamy? Or do I want to freeze individual drops and show the energy of the waves? Same water. Different shutter speed. Different photograph.

ISO

ISO is our third way of controlling the exposure. For our purposes, think of ISO as how much light we need. A lower ISO requires more light. A higher ISO allows us to work with less light.

One quick note: ISO doesn’t physically let any more light into your camera. Aperture and shutter speed do that. ISO changes how the camera uses the light it already captured. “How much light we need” is just the easiest way to think about it while you’re learning.

For example: ISO 200 requires twice as much light as ISO 400 for the same exposure. Go another step: ISO 400 requires twice as much light as ISO 800. Each time we double the ISO, we need half as much light to produce an equivalent exposure, assuming aperture and shutter speed stay the same.

But, of course… Nothing is free. Higher ISO generally comes with more image noise and can reduce image quality and dynamic range. So we don’t simply crank the ISO to whatever number we want. It’s another trade-off.

Three Controls. One Exposure.

Here’s the important part. Aperture, shutter speed and ISO all affect the amount of light required to make the photograph. Change one, and something else may need to change to compensate.

For example, you have your camera set at:
f/8, 1/125 second, ISO 100
You decide you want a faster shutter speed because your subject is moving. So you change the shutter to 1/500 second. That’s a much shorter amount of time. You’re letting in less light.

So now you have a choice. Maybe you open the aperture. Maybe you increase the ISO. Maybe you do both. Or maybe the photograph was already bright enough and nothing needs to change. That’s the whole idea. You are constantly balancing these three controls.

But Here’s Where Photography Gets Interesting

The Exposure Triangle isn’t really about getting the settings “right.” It’s about understanding what each setting does. Because you can create the same basic exposure with very different combinations.

For example, these might produce similar exposures: f/8 – 1/125 – ISO 100, or f/5.6 – 1/250 – ISO 100, or f/11 – 1/60 – ISO 100. The amount of light may be similar. But the photographs won’t necessarily look the same.

Why? Because changing the settings changes other things. The aperture changes Depth of Field. The shutter speed changes how motion is recorded. The ISO changes image quality. And that is the whole game.

Nothing Is Free

This is probably the most important idea I can teach you. Nothing is free. Want more light? You have to get it from somewhere. Want a faster shutter? You may need a wider aperture or higher ISO.

Want more Depth of Field? You may need a smaller aperture, which may require a slower shutter or higher ISO. Want the cleanest possible image? You may want to keep your ISO low, which means you need enough light or need to make another trade.

Every decision gives you something. Every decision asks you to give something back. That’s photography.

How I Think About It

When I pick up my camera, I don’t start by asking: “What settings should I use?” I start with: “What am I trying to photograph?” Then: “What does the light look like?”

I generally start at ISO 100, because I want the best image quality I can get. I’ll often start around f/8, because that’s a good starting point for the lens I’m using and the type of photography I do. Then I’ll adjust my shutter speed until I’m somewhere around the exposure the camera is telling me I need.

I say “somewhere around” because the camera meter is making its own assumptions. The meter is trying to give me an exposure based on an average. But if I’m photographing a scene that is mostly dark, like a night seascape, that average may not be what I want. That’s where the histogram comes in.

I’ll take the photograph. I’ll look at the histogram. And I’ll ask myself a very simple question: Do I need more light or less light? Then I decide which part of the triangle I want to change. That’s the difference between operating a camera and photographing.

And Then There Is the Creative Decision

Once we understand how to control the light, we get to the fun part. We get to decide what we want the photograph to look like.

Maybe I want a shallow Depth of Field. I’ll think about aperture. Maybe I want to freeze motion. I’ll think about shutter speed. Maybe I’m shooting in very low light and I can’t get the shutter speed or aperture where I want them. I’ll think about ISO.

The camera doesn’t make those decisions for me. I do.

So What Were Your Settings?

This is one of the questions photographers get asked all the time. “What were your settings?” And honestly, sometimes it makes me cringe a little. Not because it’s a bad question. But because I don’t want you to think that my settings are the recipe for making my photograph. They aren’t.

The settings are simply the result of the decisions I made at that particular moment. I might start shooting before sunrise in almost complete darkness. A few hours later, I might be shooting in full daylight. So what were my settings? All of them.

This photograph was taken somewhere in between. The tide might be different. The wind might be different. The moon might be different. There might be haze. There might be clouds. The light might be completely different. And I might want the water to look completely different.

There isn’t one correct set of numbers. There is only the photograph you’re trying to make.

Learn the Triangle

Don’t memorize settings. Understand the controls. Understand the trade-offs. Learn to ask:

Do I need more light or less light?
Do I want more Depth of Field or less?
Do I want more motion or less motion?
Do I want the cleanest possible image, or am I willing to trade some image quality for more flexibility?

Once you can answer those questions, the numbers start making sense. And once the numbers start making sense… you are no longer just taking pictures. You’re making photographs.

Learn the triangle. Then learn to make the choices.

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