Understanding How To Use The Exposure Triangle

Understanding the Exposure Triangle and how your shutter speed, aperture, and ISO are not only related but also how they affect your final image from a creative point of view, is the most valuable lesson any new photographer can learn.
Exposure Triangle Featured Image

Introduction

Most new photographers start by using their brand new camera with automatic settings. With little to no understanding of exposure or how the exposure triangle work. Only when they start getting frustrated with their images. Or when comparing them to other photographers, will they begin exploring different settings. 

Most often, they will read articles or watch videos to try and solve the problem they are having. Most of the time, these articles will solve their immediate problem. But, they still won’t have a proper understanding of how the exposure triangle works. Nor how the individual components affect the final image.

What You Need To Understand About The Exposure Triangle

The first thing that you need to understand is that it consists of three distinct components, shutter speed, aperture, and ISO. These three components combined determines the exposure value of your image.

The second thing is that these components have a different creative effect on your image. 

In this article, I will discuss both these concepts in more detail. For now, understand that shutter speed, aperture, and ISO are always related. And that you will have to balance and compromise depending on what you are trying to achieve.

Understanding The Exposure Triangle

Shutter speed, aperture, and ISO combined are known as the exposure triangle. By adjusting these components, you can alter the exposure value of a particular image. You can make the image darker by decreasing the exposure value. Or you can lighten the image by increasing the exposure value. You adjust exposure values in steps, referred to as stops. When changing your exposure, you can either use the shutter speed, aperture, or ISO. You can also do it through a combination of them, depending on how many stops you want to adjust.

How To Adjust Your Exposure Value 

You will find a mode dial on your camera that allows you to adjust the different exposure components. You need to understand what you are trying to achieve in your image, which will enable you to pick the best mode when setting your exposure. 

The first two modes you need to get familiar with are aperture and shutter priority. In these modes, you are responsible for setting the ISO and the aperture or shutter speed. Once you have set these, the camera will then calculate the third component in the triangle. Think of these two modes as semi-auto. They are handy if you care about controlling the creative effect they have on your image.

The third, and arguable the most powerful, is manual mode. As the name implies, you are in full control of setting the exposure for your image. You will have to balance ISO, shutter speed, and aperture to achieve the correct exposure.

Exposure compensation

As mentioned, when you are using shutter or aperture priority, you are only in control of two settings. ISO and either the shutter speed or the aperture. As you progress in your photography, you will start favoring one of these two modes over the other.

You might want to influence your exposure without changing the components you control. One way of doing this is to switch into manual mode, where you have control over all three components. Another way you can influence the third component is by using exposure compensation.

When using exposure compensation, you adjust the exposure value by several stops. The camera will then adjust the third component to get the desired exposure.

Using Your Histogram To Set Exposure

It can be challenging to tell if you have the correct exposure by looking at the screen on your camera. The problem you will face when you over or underexpose your image is that parts of your image become clipped. Clipping is when parts of your image turn pure white or black with no details left in those areas. You will not be able to recover those details in post-processing, and the image will be useless.

The easiest and best way to determine your exposure is to look at the histogram your camera provides. Using the histogram, you will be able to adjust your exposure to ensure you are capturing the best image.

Shutter Speed

The first component in the exposure triangle that we are going to look at is the shutter speed. It is also arguable the easiest of the three to understand when it comes to your exposure value.

City scene with car light trails

What Is Shutter Speed?

The short answer, shutter speed is nothing more than the duration that the shutter stays open. When you press the shutter button, the camera will open the shutter, allowing light to fall on the sensor. The longer you leave the shutter open, the more light, the brighter the image will be. And for a shorter duration, the less light and the darker, or more underexposed the image will be. 

You measure hutter speed in fractions of a second depicted as, 1/200s, or one two-hundredth of a second. If you want to decrease your exposure value by one stop, you should double your shutter speed to 1/400s. And if you wanted to increase your exposure, you would have to half the shutter speed to 1/100s. This will allow the shutter to stay open twice as long, letting in more light. 

Your camera will have a standardized list of shutter speeds that you can select. Some cameras, though, might allow you to adjust your shutter in half or third stops. Make sure to check your settings, so you understand by how much you are changing your exposure value. 

What Affect Does Shutter Speed Have On Your Image?

I mentioned that each of the components would have a different effect on your final image. Besides the exposure, the shutter speed affects the motion blur or lack thereof in your image. 

When you have a moving subject in the scene, you could choose to freeze the action using a faster shutter. One limitation that you might face is that all cameras have a maximum shutter speed. In most cases, you will not bump up against this value, but it is worth noting what that limit is in your camera.

On the other end, you could choose to introduce motion blur into your image. You do this by slowing down the shutter speed. When used in appropriate situations, this creates very dynamic images. Again most cameras have a limitation on how slow they can go. It is easier to overcome this, though, as most cameras also have what is know as bulb mode. Bulb mode allows you to open the shutter for as long as you want. Using bulb mode, you will have to put your camera into manual mode and set the entire exposure value by yourself. It is also good practice to use a tripod and an external remote or a timer to trigger the shutter. If not, you run the risk of introducing camera movement during the exposure.

Subject vs. Camera Movement

When shooting handheld, it is crucial to be mindful of both subject and camera movement. Once you start slowing the shutter speed, it is possible to introduce camera shake. Camera shake is not desirable in your images. It will affect sharpness and create blur across the entire photo.

Camera manufactures have implemented image stabilization into both cameras and lenses. This stabilization will help you with handholding your camera at slower shutter speeds. It is crucial to know, though, that these technologies have their limitations. They will only help reduce camera movement, not subject movement. The only way to freeze a subject is to use faster shutter speeds.

Aperture

The next component of the exposure triangle we will look at is aperture. Unless you are shooting moving subjects, this is the component that you will be using the most. It is the hardest to understand and the most confusing to adjust when first getting started.

Alleyway with shallow depth of field

What is Aperture?

Although aperture is a component of the exposure triangle, it is actually in your lens and not the camera. That is important as the lens you are using will determine the aperture range you can use. All lenses will show their aperture on the lens. 

On some zoom lenses, you will find two aperture numbers. These refer to the largest aperture based on the zoom position. Variable aperture zooms are either entry-level lenses or higher end compact zoom lenses. 

A lens contains several aperture blades that adjust the size of the opening in the lens. It changes according to the aperture you set. The bigger the aperture you set, the bigger the opening in the lens. Subsequently, more light will enter the camera, and the brighter the image will be. Stopping down the aperture will result in a smaller opening with less light and a darker image.

You measure the size of the lens aperture in f-stops, depicted as f/2.8. It refers to the ratio between the aperture diameter and the focal length of the lens. 

Remember how I said aperture is confusing, well a smaller f-stop number, refers to a wider opening of the aperture, meaning more light. Every f-stop will either allow twice or half as much light to enter the camera. So if you want to decrease the exposure by one stop from f/2.8, you would stop down to f/4. And if you want to increase the exposure by one stop, you will stop up to f/2. 

Like shutter speed, aperture also has a standardized list of f-stops. But, they are not as intuitive to remember as shutter speed. There is no simple calculation to perform to determine the next aperture. Luckily it is not a big list to remember if you want to. Like shutter speed and ISO, it is not necessary to remember them to adjust your exposure value.

How Does Aperture Affect Your image?

Have you have ever looked at an image and noticed the background is all blurred out? Sometimes you are not even able to identify any background objects. That’s because the image has a shallow depth of field. On the other side, those landscapes where everything is in focus, are using a wide depth of field.

Depth of field is the distance between the near and far objects in your scene that are in focus. Aperture is not the only factor contributing to the depth of field. Everything else being equal, though, it is the only one you have control over.

The bigger the aperture you set in the lens, the shallower the depth of field will be in the resulting image. Like I mentioned earlier, the lens you are using will determine the biggest aperture you can set. Lenses with large apertures usually get referred to as fast lenses. Because you can increase your shutter speed by using a bigger aperture, letting in more light. Be careful though, a very shallow depth of field is not always desirable. It can also be a challenge to get critical focus when using a very shallow depth of field. You can use a shallow depth of field for artistic effect or remove a distracting element. By blurring out the background elements, you will increase the focus on your main subject.

If you want to have everything in the scene in focus, you should opt for a wider depth of field or a smaller aperture. Smaller apertures present another problem to be aware of know as diffraction. Diffraction occurs in very small apertures. When the light passes through the small opening, it gets bent, causes a loss of sharpness and resolution in your images. You should test all your lenses to determine the smallest aperture you are willing to use for each lens.

Optimal aperture for your lens.

Another reason to test your lenses is to understand their optimal aperture range. Most lenses will be at their sharpest between f/5.6 and f/11. You may opt to trade some sharpness for a wider depth of field by using smaller apertures. Or you may want to blur out a distracting background element at the cost of some sharpness by stopping up to f/2.8 or f/2. Knowing the optimal aperture range for your lenses will allow you to make decisions when in the field.

ISO-Film Speed

The last component of the exposure triangle is ISO. ISO is a hangover from the film era. Commonly referred to as film speed, it measures the photographic film’s sensitivity to light.

Night city scene with no noise

What ISO?

Generally, when buying photographic film, you would buy according to the film speed. Once you loaded the film into the camera, you would have to shoot the entire roll. The only way to change the film speed is by loading a new roll with a different speed. Usually, the speed you would choose is dependent on the subject you plan on shooting.

You can take this basic concept and refer to ISO as the sensitivity to light of your digital sensor. By increasing the ISO value, you can make the sensor more sensitive to light. And by decreasing, you will make the sensor less sensitive. 

The history of measuring film speed is long and complicated. The current ISO standard is, in fact, a combination of two older standards. You measure ISO using a linear arithmetic scale with “ISO 100” being the most common lowest value. Being a linear scale, “ISO 400” will double the amount of light from “ISO 200” and “ISO100” will reduce the amount of light by half. Some higher-end cameras also offer ISO values lower than “ISO 100”. These lower ISO’s could be native or in an expanded mode. Be careful, though, when using expanded mode as it may affect your image quality. 

The Good, The Bad, And The Ugly About ISO.

To be honest, there isn’t much good about ISO. Other than you no longer have to shoot the entire roll of film before being able to change it. You no longer have to know what your subject will be before loading your film, or compromising if you didn’t know.

What compromise would you have to make? Well, when talking about a roll of film, the bad comes in the form of grain. You see, silver halide crystals cover the film emulsion. The size of the crystals determines the speed of the film. Larger crystals make the film more sensitive to light, producing a faster film. And the finer the crystals, the less sensitive and slower the film will be. When looking at an image captured on film, you can see the grain structure in the final image. Larger crystals, or faster film, will produce much more grain in the image. Many digital photographers try to emulate this grain by replicating it during post-processing.

The ugly part of increasing sensitivity to light at will is digital noise. Noise, unlike grain on film, is not very pleasing. It causes the loss of details and also affects the dynamic range of the sensor. All cameras handle or create noise differently. If shooting in low light is something you often plan to do, I would look at the cameras’ low light performance. It is possible to remove noise during post-processing. But it will also ruin the details in your image, so use noise reduction only where needed. 

Auto ISO

I mentioned earlier that when in shutter or aperture priority, you will have to set the ISO. There may be times where all you care about is setting either your shutter speed or the aperture. You can do that by using Auto ISO.

Imagine you are shooting an event in low light, and you are using aperture priority. Usually, you would choose the aperture based on the depth of field you want in your image. You would select an ISO value that will allow the camera to set a high enough shutter speed. The problem with this is that you will have to watch your shutter speed to ensure it is fast enough. And you will have to adjust your ISO or aperture if it is not.

Auto ISO allows you to tell the camera your preferred ISO, which would generally be a low value. You will also tell it your lowest acceptable shutter speed to avoid motion blur. The camera will then use the preferred ISO until the shutter speed drops below the lowest speed. When that happens, the camera will begin increasing the ISO to maintain that shutter. It will also lower the ISO again once the shutter speed goes above the lowest shutter speed.

Using auto ISO allows you to focus on your composition and the creative effect of your image. It is useful in a fast-paced environment where it might not be possible to take a second shot.

Conclusion

Understanding the exposure triangle requires you to first decide on your exposure value. This will ensure that you have the correct exposure for the current scene in front of you. Using your camera’s histogram is the best way of ensuring that you have the right exposure.

When setting the exposure, you need to keep in mind what look you want in your final image. You need to remember how each of the three components will affect your final image.

  • Shutter speed controls how long the shutter stays open. You can use it to create artistic motion blur in your image.
  • Aperture controls the size of the opening in the lens and determines your depth of field.
  • ISO controls the camera’s sensitivity to light, and will introduce noise the higher you set it.

When shooting, I try and shoot at the lowest ISO setting possible. This ensures that I will have as little noise in my images as possible.

In most cases, I give priority to my aperture so I can control the depth of field of the image. Like most, I favor a wide depth of field in my landscapes and a shallower depth of field in portraits.

There are two occasions where I will give priority to my shutter speed. The first being when I want to introduce some motion in landscapes like long exposures. In this case, I will always be using a tripod to get slow shutter speeds. On the second occasion, I will use a faster shutter speed when I want to ensure I am freezing motion. Generally, when shooting things like wildlife or my kids playing.

Learning to set your exposure is one of the most basic and valuable skills that you can learn as a photographer. The key to mastering the exposure triangle is to go out and shoot with the intent of practicing.

Over To You

I hope this article has helped you to understand the exposure triangle some more. If you want to know more about exposure, aperture, shutter speed, or ISO, let me know in the comments below.

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One Response

  1. As someone who shoots a lot of landscapes, I mostly use a wide aperture. I also use slow shutter speeds for long exposures quit often. The combination of these two tend to produce the most visually pleasing images to me. What is your favourite settings?

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