The Exposure Triangle
The Exposure Triangle is a fundamental concept of photography. It helps you to control the exposure of your images, which affects the brightness, sharpness, depth of field, motion blur, and noise level. By understanding how to balance three camera settings, you not only will be able to create correctly exposed images, but you can also create different effects and express your artistic vision.
In this comprehensive article, you’ll learn what the exposure triangle is and how you can benefit from understanding it. It covers:
What is the Exposure Triangle?
How to balance the Exposure Triangle?
How to use the Exposure Triangle creatively?
What is the most important setting in the Exposure Triangle?
Do you need a perfectly balanced Exposure Triangle?
Do you need to understand the Exposure Triangle when shooting in automatic mode?
What is the Exposure Triangle?
The exposure triangle is a term that describes how shutter speed, aperture and ISO work together to control the amount of light that reaches the camera sensor. Changing one of these settings affects the other two, so you need to balance them to get the desired exposure.
What are the Exposure Triangle settings?
The three settings of the exposure triangle are:
Aperture: The size of the opening of the lens that lets light in. It affects the depth of field and the amount of background blur.
Shutter Speed: The length of time the camera sensor is exposed to light. It affects the motion blur and the sharpness of moving subjects.
ISO: The sensitivity of the camera sensor to light. It affects the noise level and the graininess of the image.
These settings are interrelated, so changing one of them affects the others and the overall exposure.
Aperture
The first camera setting in the exposure triangle is the Aperture. This setting refers to the opening in which light enters through your camera’s lens and is measured in f-stops, such as f/2.8, f/5.6, f/11, or f/22.
A lower f-stop number (such as f/2.8) corresponds to a larger opening, allowing more light to enter the camera. A higher number (such as f/22) corresponds to a smaller opening, allowing less light to enter the camera.
Aperture also affects the Depth of Field, which is the range of sharpness in a photograph. It is the distance between the nearest and the farthest objects in a photo that are in acceptably sharp focus.
A large aperture (small f-stop) creates a shallow depth of field, meaning only a small part of the image is in focus, while a small aperture (large f-stop) creates a deep depth of field, meaning most of the image is in focus.
Also, you should be aware that lenses are typically the sharpest in the middle of their aperture range (called the lens’s ‘sweet spot’), and not at their widest or smallest aperture.
When photographing a grand landscape, the aperture should typically be in the f/8-f/13 range to have acceptable sharpness throughout the image that also happens to be the sweet spot (or thereabouts) of most lenses.
Apart from aperture, there are other factors that influence the depth of field namely the focal length and the distance to the subject.
Shutter Speed
The second camera setting in the exposure triangle is the Shutter Speed. Shutter speed is the length of time the camera shutter is open, exposing light onto the camera sensor. This duration is measured in seconds or fractions of seconds.
It affects the amount of light the camera takes in, as well as the motion blur and the sharpness of moving subjects. A fast shutter speed (short exposure) such as 1/2000th of a second freezes the motion and creates a sharp image, while a slow shutter speed (long exposure) such as 1/4th of a second blurs the motion and creates a smooth image.
The longer the Shutter Speed, the more light the camera will capture, and vice versa. However, you need to be aware that a longer exposure time means the camera registers more motion. Whether it’s from camera vibration or a moving element within the frame, it will show in the final image. That is why you can’t simply use a longer shutter speed to make a brighter exposure without taking the proper precautions (such as using a tripod).
A general rule of thumb for a shutter speed capturing a grand landscape is to not go below 1/focal length (e.g. 1/30th for a 30mm lens) when photographing handheld. See further down for a detailed explanation.
ISO
ISO is a camera setting that controls the sensitivity of the camera sensor to light*. It affects the brightness and the noise level of the image. A high ISO (high sensitivity) makes the image brighter and more noisy, while a low ISO (low sensitivity) makes the image darker and less noisy.
It is measured using numbers such as ISO100, ISO200, ISO400, ISO1600, etc.
*Note that this is not strictly true, because you can’t change the sensitivity of the sensor. It would be more precise to say that ISO determines the in-camera amplification of light information produced by a specific scene luminance, aperture, and shutter speed. But I hope you don’t mind that I continue to refer to an ISO setting as controlling the light sensitivity.
As you’ve learned by now, there’s always another factor to consider. While a higher ISO makes the camera more light-sensitive, it also introduces digital noise or grain to the photo. The higher the ISO, the more noise becomes visible. The exact value at which noise becomes problematic will depend on the camera (and the post-processing software) that you’re using.
You should aim to keep your ISO setting as low as possible.
Connecting the settings
So how are these settings impacting each other? Let’s imagine we’re filling a bucket of water. The bucket represents the camera sensor, the water represents the light, and the exposure represents how full the bucket is.
Aperture: The size of the hose that fills the bucket. A large hose (large aperture) fills the bucket faster, while a small hose (small aperture) fills the bucket slower.
Shutter Speed: The time that the hose is turned on. A short time (fast shutter speed) fills the bucket less, while a long time (slow shutter speed) fills the bucket more.
ISO: A filter on top of the bucket that stops dirt from entering the bucket. A fine filter (low ISO) lets through less dirt and causes the bucket to fill slower, while a coarse filter (high ISO) lets through more dirt and causes the bucket to fill faster.
In photography terms:
The larger aperture you have (such as f/2.8), the quicker shutter speed you need to get a correctly exposed image.
The smaller aperture you have (such as f/11), the slower shutter speed you need to get a correctly exposed image.
The lower ISO you have (such as ISO100), the fewer grain and noise will be present in the image with an overall higher quality.
The higher ISO you have (such as ISO1600), the more grain and noise will be present in the image with an overall lower quality.
Balancing the Exposure Triangle
The exposure triangle method enables you to get all three elements (aperture, shutter speed and ISO) working together to produce a photo that is properly exposed. This means that the photo is neither too bright nor too dark, and has the desired effect of depth of field, motion blur and noise level.
To balance the exposure triangle, you need to adjust one or more of the elements to compensate for the changes in the others. For example, if you increase the aperture (large opening), you need to decrease the shutter speed (fast shutter) or the ISO (low sensitivity) or both to keep the same exposure value.
At this point, you need to understand what is meant by Exposure Stops, so I’ll quickly explain what this refers to.
An Exposure Stop (or simply Stop) refers to the doubling or halving of light that reaches the sensor. Stops are an important factor in balancing the exposure triangle. When you adjust one side, you’ll need to compensate on one of the other. Suppose you change the aperture with one stop (going from f/4 to f/2.8 doubles the amount of light). In that case, you need to compensate for one stop by either using a quicker shutter speed (going from 1/60th to 1/125th) or a lower ISO (going from 200 ISO to 100 ISO).
Using the Exposure Triangle creatively
There are three elements to consider in relation to the exposure triangle that impact the creative side of photography. These are:
Depth of Field: The aperture determines the range of sharpness in the image. You can use a shallow depth of field (a large aperture such as f/2.8) to separate the subject from the foreground and background, while you can use a deep depth of field (a small aperture such as f/22) to make everything in focus. Landscape photographers typically try to create an image that’s sharp throughout and use a small aperture without sacrificing sharpness (i.e. they avoid shooting with f/22 when they can). You can create a sun star when shooting towards the sun with a small aperture (but make sure your lens is clean 😊).
Motion: The shutter speed determines the amount of blur in the image. You can blur moving objects (such as water, clouds and fog) with a slow shutter speed, while you can freeze moving objects (such as animals, people, leaves and waves) with a fast shutter speed. Slow shutter speeds enable you to create soft textures in water and clouds, light trails of vehicles, and star trails. And you could try out some ICM (intentional camera movement). Fast shutter speeds enable you to create sharp grasses and leaves in the foreground when it's windy, details of birds in flight, wave details, etc.
Grain: The ISO determines the degree of grain in the image. You get more grain the higher the ISO. Note that this is hardly used in landscape photography, and a grain effect, if desired, is typically added during post-processing.
What is the most important setting in the Exposure Triangle?
There are no specific settings to create the perfect exposure. It all depends on the situation and the kind of image you want to create. Different genres of photography have different priorities, and within that genre, many factors need to be considered depending on what you’re photographing.
For instance, these are common scenarios in landscape and nature photography:
When photographing a grand landscape, you typically want an aperture between f/8 and f/13, as this gives you the best front-to-back sharpness. The ISO should remain as low as possible to minimise the amount of noise, which means you should adjust the shutter speed to get a perfect exposure. If wind is making the leaves or grass in the foreground move too much, you may need to increase the shutter speed and ISO to avoid blurring any moving elements within the frame.
When photographing flowing water, you typically want a slow shutter speed between 1/8th and a few seconds to show movement. Even slower if you want to create very smooth water. This means you should adjust your aperture to get a good exposure. It also means that you typically want to use a tripod (and you may need to use a neutral density filter).
When photographing animals such as birds in flight, you need a quick shutter speed, such as 1/4000th of a second. In this case, you can achieve that by using a wide aperture such as f/2.8 and increasing the ISO until the exposure triangle is balanced.
When photographing the night sky, you typically need a wide aperture, slow shutter speed, and high ISO. Here, the ISO is often adjusted as the two other components should be more fixed.
As you can see, there isn’t a most important setting in the exposure triangle. They all play equally important roles in creating a well-exposed image. However, there are some general rules of thumb that I use for landscape photography:
ISO should be as low as possible. I use ISO100 as the base setting.
Aperture should be between f/8 and f/13. My default setting for landscapes is f/11.
Shutter speed should not go below 1/focal length when photographing handheld*. For example, when shooting with a 15mm wide angle lens, the shutter speed should not be below 1/15th of a second, and when shooting with a 400mm tele lens, the shutter speed should not be below 1/400th of a second.
If the image is too dark when shooting with the preferred aperture and shutter speeds, I’ll increase the ISO or use a tripod. I regularly go up to ISO 400-800 for landscape images without losing too much quality, especially when using the noise reduction features in post-processing software such as Adobe Lightroom and Topaz DeNoise AI.
*Note that Image Stablisation is rapidly improving, which enables slower shutter speeds to be used while still getting sharp images. Trial and error is the best way to know your equipment.
Do you need a perfectly balanced Exposure Triangle?
One of the significant advantages of digital cameras is that it’s not necessary to perfectly expose the image in camera. You’ll be able to make substantial changes to the exposure in post-processing using software like Adobe Lightroom.
This means that if you must choose in the field between under-exposing or blurring an image, you can choose to under-expose and fix it later (you can’t fix a blurry image). Although, significant under exposure will likely increase noise, thus impacting the image quality.
Does that mean that you can ignore the exposure triangle? No, you should always be aware of your camera settings, be aware of the potential consequences of those settings, as failing to do so can severely damage the image quality or impact your ability to realise your photographic intent.
Do you need to understand this when shooting in automatic mode?
Digital cameras have a built-in light meter that measures how much light is coming from a specific scene. When setting your camera to an automatic shooting mode your camera will choose one or all three of the settings for you. For instance, the Aperture Priority Mode enables you to choose the aperture and ISO while the camera picks the shutter speed to create a well-exposed image according to its light meter. This is a very convenient shooting mode for landscape photography (and I use it a lot).
Does that mean that you can ignore the exposure triangle? No, although your camera will take care of the exposure (and will get it right most of the time), you should always be aware of your camera settings to ensure that you get the right depth of field and sharp moving objects (or motion blur, if desired) to realise your photographic intent.
Conclusion
The Exposure Triangle is a term that describes how three camera settings, shutter speed, aperture, and ISO, all have an impact on the exposure of an image. Changing one setting has a direct impact on the others. Understanding how these settings are connected enables you to:
Create a well-exposed image by balancing these settings.
Be creative when taking a photo by using these settings to affect depth of field and motion blur.
No longer need to rely on an automatic mode that values technicality over creativity, but instead take control of the image-making process.
The best way to learn how these settings impact the image is to try them out in the field and compare the results in your favourite post-processing software (such as Adobe Lightroom) to see how adjusting one or the other affects the exposure and quality of the image.
Have fun shooting and please let me know in the comments if you have questions or feedback.