Diagram showing the exposure triangle

Exposure Triangle | Ultimate Guide On How To Properly Expose Photos

Have you ever heard photographers talking about the exposure triangle and wondered what they mean?

It’s one of those concepts that’s often talked about but can seem unfathomable to new photographers. With words like triangle involved it might even sound like a lesson in advanced mathematics, but fear not!

Long-exposure photo at sunset
An understanding of the exposure triangle is critical for taking decent photography like these. It gives you several tools to control your exposure just the way you want.

Let’s start off by looking at the basics of exposure and the mists should begin to clear…

After reading this article, you will be able to ‘communicate’ with your camera so that it understands your creative exposure needs.

What is Exposure?

At its most basic level, exposure is the amount of light reaching the image sensor of your camera. It is determined by three factors shutter speed, aperture, and ISO (film sensitivity to light)

If you stick your camera in automatic mode it will guess which combination of the above three settings is needed to achieve the correct exposure for the scene.

Often, it’ll do a poor job. That is why you should take control of things.

If you capture this scene in auto mode, it’ll most likely underexpose to compensate for the bright sky. Which will result in lost shadows (too dark foreground)

What is the Exposure Triangle?

Exposure triangle explains how the exposure of an image is effected by three fundamental properties of a camera: Aperture, Shutter Speed, and ISO.

If you want to do any creative photography, adjusting and understanding these fundamental properties is a must.

Exposure triangle explains how each of these three properties is interconnected.

therefore, if you understand the exposure triangle, you are able to dial up one property while dialing down the other to keep both your exposure and artistic needs satisfied.

Diagram showing the exposure triangle
Exposure triangle explains how ISO, Shutter Speed, and Aperture are interconnected

Before you try to understand the exposure triangle, let’s understand the three properties first…

1. Aperture

Inside your lens is an iris which expands and contracts to let more or less light through.

Think of it like the pupils in your eyes, which become smaller in bright conditions and expand in dark places to let more light in.

A camera lens with aperture hole showing
In this picture, you can clearly see the blades that create the lens’s aperture. Photo by Dan Gold.

The different apertures are classified by a series of F-numbers (often known as f-stops)–f/2, f/2.8, f/4, f/5.6, etc.

To the uninitiated, these numbers may appear as a somewhat random collection of numbers. But they actually refer to the relationship between the focal length of your lens and the diameter of its aperture.

f-stop calculation formula

At a basic level, all you need to remember is this…

A large aperture = small f-number (f/2.8) = more light

A small aperture = large f-number (f/11) = less light.

That’s pretty logical really!

As you make your aperture smaller, the amount of light reaching the sensor (exposure) is reduced

Aperture not only affects the exposure but also affects the depth of field–giving you the artistic freedom to isolate your subject with creamy bokeh. To learn more about aperture, please read our in-depth aperture guide.

2. Shutter Speed

Your shutter speed determines how long your camera’s sensor is exposed to the light.

shutter speed determines how long the shutter stays open. As a result, it controls how much light as well as how much motion is captured in your shutter.

If your shutter speed is 1/1000th of a second, your camera only exposes the sensor to light for 1/1000 of a second. That’s barely any time at all so only a tiny amount of light will get through.

By contrast, most cameras can hold the shutter open for as long as thirty seconds – time enough to let in masses of light!

As you make the shutter speed faster (left to right), the exposure is reduced.

Shutter speed also gives you the creative freedom to either freeze or capture motion in your photography. Use fast shutter speed to freeze the motion of a subject. Or use slow shutter speed to capture motion.

Here’s a series of pictures to illustrate my point, all of which were created by varying only the shutter speed.

As you slow down the shutter speed (from left to right) the motion of the river is captured for a longer period. The slowest shutter speed (lower right) creates a silky smooth water effect. Photos by Helen Hooker

To learn more about shutter speed, have a look at our in-depth shutter speed guide.

3. ISO

ISO is the sensitivity of your camera’s sensor to light.

Increasing ISO allows you to capture photos in low light without having to keep your shutter open for too long. A handy trick for taking photos in low light conditions without a tripod.

At ISO 100 the sensor is at its least sensitive. This means you’ll need to keep your shutter open for longer.

Taken to the opposite extreme, at ISO 3200 the sensor is five times more sensitive so you’ll only have to open the shutter for a short length of time to capture the same amount of light. This can be really handy in dark places, especially if you’re not able to use a tripod.

As your ISO increase, the sensor becomes more sensitive to light. Thus, increasing ISO makes your photos brighter.

Increasing ISO sensitivity of your sensor allows you to shoot in darker places. This can be immensely helpful at low light conditions. However. if you increase ISO too much it will introduce digital noise (grains) to your images. To learn more about ISO, check our camera ISO guide.

How Aperture, ISO, and Shutterspeed Interrelate.

Here is a simple exercise for you to truly understand how the exposure triangle works. Set your camera to manual mode and follow along.

Take a photo with: ISO 200, Aperture of f5.6, and Shutter speed of 1/200s.

Experiment 1: Changing One Side of the Exposure Triangle

Now increase your aperture to f8 and shoot the same picture again. Do you notice how the resulting picture is darker? This is because we’ve made our aperture smaller but the other settings have remained the same. As a result, less light reached the camera’s sensor–so the picture is darker.

By doing this, we’re changing one ‘side’ of the exposure triangle and you can see a visible difference.

Let’s see if we can get the exposure back to the original photo’s level by changing a different setting now.

Experiment 2: Using the Other Two Sides to Compensate

Leave your aperture at f8, but this time reduce your shutter speed to 1/100 of a second and shoot again. The resulting image should look much more like your first shot. This is because you’ve increased the amount of light reaching the sensor by opening the shutter for twice as long – this compensates for the smaller aperture.

Of course, you could have increased your ISO from 200 to 400 and achieved the same result.

What Did We Learn?

This exercise shows how changing one side of the exposure triangle will require you to change one of the other sides too if you’re going to achieve the same exposure.

Easy Way to Understand the Exposure Triangle

There is an easier way to set up your camera to understand the exposure triangle. If you set the camera to one-third stops, you don’t even need to worry about the numbers. As you turn the various dials on your camera now all you need to remember is that for a one whole ‘stop’ of exposure you simply turn the dial in question by 3 clicks.

So, for the example I gave above, you’d turn your aperture dial-up by three clicks to move from f5.6 to f8. Conversely, the shutter speed needs to be dialed down by 3 clicks from 1/200 to 1/100 to keep the same exposure.

As you can see, this removes some of the maths from the exercise and makes it a more logical process. Access your camera menu and look for references to ISO and aperture increments. For either or both of these, you’ll have an option to set either 1EV increments or 1/3 stop increments.

Why the Exposure Triangle Is Important?

Mastering the three sides of the exposure triangle and understanding how they are interrelated helps you perfectly expose your photos.

Perhaps even more importantly, it is essential for artistic expression. You may want a creamy bokeh effect, freeze motion, or shoot in low light.

Knowing the exposure triangle allows you to satisfy these creative needs while still correctly exposing your photos.

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About the author

Helen Hooker

Helen Hooker is a musician and photographer based in the UK. Helen has been photoblogging every single day since November 2008 and has a particular passion for architectural and wildlife photography.

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