The Exposure Triangle Explained

The Exposure Triangle Explained: how Shutter Speed, Aperture and ISO work together

The exposure triangle may sound like a complex piece of mysterious photography knowledge, particularly if you are moving your first steps into using your camera in manual mode.

Don’t worry, it’s a pretty simple concept once you get a handle on what it means and how it works.

As a matter of fact, you've probably already begun to learn about it without realizing it.

The three main points that make up the exposure triangle are the three most important settings on your camera: aperture, shutter speed, and ISO.

We promise that we won't get too technical, but by the time you're done reading you'll understand the basics of the exposure triangle.

Infographic

Exposure Triangle Infographic

The Basics of Exposure

If you're just starting to explore using Manual Mode on your camera, the first thing you need to know is that aperture, shutter speed and ISO all work together to determine the exposure of your photograph.

What is the Exposure

The simplest way to define exposure in photography is "the measure of how bright or dark an image is".

An image that is too bright to see everything is known as an overexposed image, because too much light was captured.

An image that's too dark to see anything is known as an underexposed image, because not enough light was captured.

A Metaphor

The easiest way to think about the three main settings is to use the analogy of imagining that you're sitting in a room with a tinted window on a sunny day.

You've got blackout curtains covering over the window letting in no light.

Taking a photograph is what happens when you open the curtains and expose your eyes - or the camera's sensor - to the light outside.

Your aperture setting corresponds to how large the window is.

Your shutter speed corresponds with how long you open the curtains for.

Your ISO setting corresponds to how dark the window tint is.

All of them together affect just what you'll see out of the window.

The window metaphor may not be the most original way to explain the Exposure Triangle, but it gives the idea of how aperture, shutter speed and ISO work together.

See other metaphors that may help you to grasp the concept.

Now that you know the very basics, let's dig a bit deeper into each of the settings to learn how they work and the different effects caused by changing them.

Aperture

Aperture simply means 'opening', and in photography it refers to the size of the opening within your camera lens that lets light reach the sensor.

The width of your aperture is measured in 'f-numbers', more commonly known as 'f-stops'.

The smaller the number is, the larger the width of the aperture is.

Most commercially available lenses have ranges between f/1.4 and f/32, with f/1.4 being the widest opening and f/32 being the narrowest, although your lens may only be able to reach a smaller section of the total possible range.

Depth of Field

As well as affecting how much light passes through the lens, your aperture setting also affects something known as 'depth of field'.

The Depth of Field, often referred to as DOF, is the area of your photograph in front of and behind the focal point that is acceptably sharp and still in focus.

A very wide aperture such as f/1.4 will have a very narrow depth of field.

That means that if you were to photograph a person's face at f/1.4 you might only get the tip of their nose properly in focus.

If you shot at a narrower aperture of f/11 or f/16 you would get a wider depth of field.

That is you would be able to get their entire face and most of the background within the depth of field and it would all look sharply focused.

Light Refraction

Without getting too technical about light refraction and the science of optics, most lenses do not perform their best at their widest aperture or their narrowest aperture unless it's an extremely high quality professional lens.

Check out this post by the guys at Fstoppers.com if you want to go deeper into technical.

Shooting at these extremes can create a number of optical problems such as softer, less focused images, vignetting (where the corners of the image are darker than the center) and other kinds of optical issues.

This is usually fixed by avoiding the extremes, but sometimes it's worth the trade-off if you want to get the narrowest or widest depth of field possible for your lens.

Pro Tip: The Lens "Sweet Spot"

All lenses have an aperture setting where they get the sharpest possible focus, a setting known as the 'sweet spot'.

As a rule of thumb, the sweet spot for most lenses is two or three f-stops below the widest aperture possible, although this sometimes changes depending on the lens.

This means that if your lens has a maximum aperture of f/1.4, the sweet spot for the lens should be around f/2.8 or f/4, depending on the lens.

Learning the sweet spot for your favorite lenses is a good habit to get into, and you can experiment with it yourself or find a chart online specific to the exact lens you're using.

If you want to learn more on how to find your lens Sweet Spot, check out this post by Digital Photography School

Some lenses don't exactly correspond to the general rule above, and others are sharp throughout their whole aperture range.

Learning the ins and outs of your lenses will definitely make you a better photographer!

Shutter Speed

The second part of the exposure triangle is shutter speed.

It controls exactly how long the shutter stays open and exposing the sensor to light.

Shutter speeds can range from 1/8000th of a second to 8 seconds to 8 hours, although if you kept your shutter open for too long you're almost sure to have an overexposed image no matter what you're photographing.

The most important thing that shutter speed does from a composition perspective is that it allows you to control the way motion appears in your photographs.

One of the most popular demonstrations of this is a classic of landscape photography.

The long-exposure waterfall shot, where the water has blurred into ghostly fog and the rest of the image is perfectly sharp.

exposure triangle

They tend to use a shutter speed of somewhere between 5 to 15 seconds in order to allow enough of the water's movement to be registered by the sensor.

The downside to this motion effect is that if you try to handhold your camera during photo with a shutter speed slower than 1/60th of a second, you're probably going to start getting motion blur.

For these shots, such as the waterfall example above, you need to use a tripod or other image stabilization technique to remove any camera shake and ensure the non-moving parts of your scene stay sharply in focus.

ISO

Your ISO setting is a measure of just how sensitive to light your camera's digital sensor is.

The digital sensor is equivalent to the film negative used in non-digital cameras.

It ranges from ISO 50 at the least sensitive to ISO 3,800,000 or more.

High ISO is extremely sensitive to light and allows you to shoot without a tripod in extremely low-light settings.

Increasing your ISO setting can be extremely helpful when a photograph that requires a specific shutter speed and aperture combination at which the photo is still too underexposed to be acceptable.

Noise

The tradeoff to having an incredibly high ISO is that the more sensitive the sensor is to light, the more mistakes it makes.

exposure triangle

These mistakes are referred to as 'noise' or 'digital noise'.

Noise looks essentially similar to the film grain found in older movies.

The higher your ISO setting, the noisier/grainier your final photograph will be.

If your camera's maximum ISO is 1600, it will probably be extremely noisy.

A newer camera with an incredibly high maximum ISO will create a much better image at the same ISO setting.

In general, it's a good idea to keep your ISO setting as low as possible in order to minimize the amount of noise in your images.

Sometimes, you have to make the tradeoff of using a higher ISO setting in order to get a proper exposure for your desired aperture and shutter speed combination.

It's up to you to determine what balance of settings will create the photograph you want with the proper exposure.

Exposure Values: How the Three Settings Learned to Play Nice Together

So your aperture, your shutter speed and your ISO settings all play a part in how much light winds up in your final image.

In order to get the perfect exposure you have to balance all three against each other.

If you narrow your aperture setting to increase your depth of field, you reduce the amount of light reaching the camera sensor.

You the have to either decrease your shutter speed or your increase your ISO to keep the same amount of light in the image.

If you want to have a long exposure during daylight, such as a blurred waterfall, you need to decrease your aperture width and your ISO sensitivity setting to reduce the amount of light in the image and maintain the proper exposure.

This is the triangle of exposure - you can't modify one of the three elements without adjusting one or both of the others to compensate and prevent your image from being overexposed or underexposed.

But since each element is measured in a slightly different way, how do you know how much to adjust each one by?

It's easy once you start thinking of things in exposure values (EV), which are unfortunately a bit confusingly also referred to as 'stops'.

Examples

For example, imagine you had a proper exposure with an aperture of f/2, a shutter speed of 1/250th of a second, and an ISO setting of 100 - but you want to switch your aperture to f/2.8 to increase the depth of field.

Changing your aperture from f/2 to f/2.8 is the equivalent of 1 stop of light, and since you are narrowing the width of the aperture you are reducing the amount of light in your image by 1 stop.

In order to bring it back up to a proper exposure of, you need to add 1 stop using either your shutter speed or your ISO setting.

You could use a longer shutter speed, changing from 1/250th of a second to 1/125th of a second or increase the sensitivity of your sensor from ISO 100 to ISO 200, both of which are equivalent to adding 1 stop.

Exposure Triangle Cheat Sheet

For your convenience, we've put together a simple exposure triangle cheat sheet in the infographic at the beginning of this post that should help make it easier for you to convert between the different units.

Each of these settings represents a difference of 1 stop from the previous number.

Your camera and lens may have smaller steps, which correspond to either one-half or one-third of an EV unit.

Pro Tip: The Sunny 16 Rule

One of the simplest ways to get a proper exposure on a sunny day is to use what's known as the 'Sunny 16' rule.

It says that if you set your aperture to f/16, you'll get a proper exposure by matching your shutter speed to your ISO setting.

For example, if you shoot at f/16, 1/100s and ISO 100, you'll get a proper exposure, or 1/400s and ISO 400, and so on, which can be extremely useful if you need to freeze motion by using a fast shutter speed but you need the extra light.

Conclusion

The simplest way to do exposure compensations in your head to simply to memorize the sequences, although even professional photographers tend to do a little bit of exposure compensation during the middle of shooting as they review their work on their camera screen.

Remember, that your available range might be larger or smaller than what you see below depending on your particular lens and camera.

That's all there really is to understanding what the exposure triangle refers to, and how the different aspects work together to create your final image.

The Exposure Triangle Explained

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About the Author Luca

Hi, I am Luca, founder and editor in chief at photographyambition.com. I am crazy about photography and I always have a camera with me. When I am not busy with my day job, enjoying my family or taking photos, I am on Photography Ambition to share what I have learnt so far.

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