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 different components of the exposure triangle work. Only when they start getting frustrated with their images, not looking the way they want, or comparing them to other photographers, will they begin exploring the different settings their camera offers.

Most often, they will read articles or watch videos trying to solve the problem they are having, like a blurry subject or that everything is in focus when they want to isolate the subject. Most of the time, these articles will solve their immediate problem. However, they still won’t have a proper understanding of how the exposure triangle works or how the individual components affect the final image.

What You Need To Understand About The Exposure Triangle

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

The second thing you need to understand is that each of these components also has a different creative effect on your final 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 constantly have to balance and compromise depending on what you are trying to achieve.

Understanding The Exposure Triangle

As mentioned earlier, the shutter speed, aperture, and ISO of your camera combined are what is know 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. Exposure values are adjusted in steps and commonly referred to as stops. When changing your exposure, you can either use the shutter speed, aperture, or ISO to stop our exposure up or down. 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

On your camera, you will find a mode dial that will allow you the adjust the different components of your exposure. It is essential to understand what you are trying to achieve in your image, as this 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, respectively. Once you have set these, the camera will then calculate the third component in the triangle for you. Think of these two modes as semi-auto, and they are handy if you only care about controlling the individual setting due to the creative effect it has 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 both the correct exposure value and the creative effect you have in mind for your image.

Exposure compensation

As mentioned above, 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 career, you will most likely start favoring one of these two modes over the other, depending on what type of photography you do.

Sometimes you may want to influence the default camera exposure value without change the settings you have control over. One way of doing this is obviously 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 are not able to directly set the third value, but you can tell the camera that you want to increase or decrease the exposure value by several stops. The camera will then adjust the third component accordingly.

Using Your Histogram To Set Exposure

Whether you are using one of the two priority modes or manual mode, it can be quite challenging to tell if you have correctly exposed your image just by looking through the viewfinder or at the screen on the back of the camera. The problem you face when you over or underexpose your image is that large parts of your image become 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. By using the histogram, you will be able to implement several different exposure techniques to ensure you are capturing the best exposure to use for post-processing.

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 in the camera 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 the inverse is valid 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 using the shutter, you should double your shutter speed to 1/400s. And if you wanted to increase your exposure, you would half the shutter speed to 1/100s, allowing 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 also to adjust your shutter in half or third stops, so check your settings to 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 three components in the exposure triangle would affect your final image differently in addition to the exposure value. Shutter speed is responsible for the motion blur or lack thereof in your image.

When you have a subject that is moving in the scene, you could choose to freeze the action by 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 maximum, 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 by slowing down the shutter speed. Long exposure is a great technique that can help create a very dynamic image when used in an appropriate situation. 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, the catch though, you will have to put your camera into manual mode and set the entire exposure value by your self. It is also good practice to use a tripod and an external remote or a timer to trigger the shutter instead of holding the shutter button, or you could risk introducing camera movement during the exposure.

Subject vs. Camera Movement

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

Camera manufactures have implemented image stabilization into both cameras and lenses to help you with handholding your camera at slower shutter speeds. It is crucial to know, though, that these technologies have their limitations, and 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 regularly, this is the component that you will be concerned with the most for the majority of your photography. It is probably 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 found 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 indicate their maximum aperture on the lens.

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

The lens will contain several aperture blades that will adjust the size of the opening in the lens according to the aperture you set. The bigger the aperture you set, the bigger the opening in the lens, the 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.

Just like shutter speed, aperture also has a standardized list of f-stops. However, 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, however just like shutter speed and ISO, it is not strictly necessary to remember them to understand and 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, and you are not 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 seemingly in focus, are using a wide depth of field.

The depth of field is the distance between the nearest and the furthest object in your scene that is acceptably sharp. Although aperture is not the only factor contributing to the depth of field, everything else being equal in the composition, it is the only one you have control over while setting your exposure.

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, based on the fact that you can increase your shutter speed due to letting in more light with a bigger aperture. Be careful though, a very shallow depth of field is not always desirable, and it can also be a challenge to get critical focus when using a very shallow depth of field. A shallow depth of field can be used as an artistic choice, but can also be used to remove distracting elements from the background by blurring them out.

If you want to have everything in the scene in focus, you will typically opt for a wider depth of field or a smaller aperture. Smaller apertures present another problem to be aware of know as diffraction. Diffraction generally occurs in very small apertures where the light passing through the opening is slightly bent, causing a loss of sharpness and resolution in your images. I would suggest testing with all of your lenses to determine the smallest aperture you are willing to use for each lens.

Optimal aperture for your lens.

Another good reason to test all of your lenses is to understand your particular lens optimal aperture range. Even though most lenses will be at their sharpest between f/5.6 and f/8, you may opt to trade some resolution for a wider depth of field by using f/11 or even f/16 depending on where diffraction starts for your particular lens. Or you may want to blur out a distracting background element at the cost of a bit of sharpness by stopping up to f/2.8 or f/2. Knowing at what aperture your lenses perform their best will allow you to make critical decisions in the field as opposed to being disappointed when getting back to your computer.

ISO-Film Speed

The last component of the exposure triangle is ISO. ISO is a hangover from the film era and was used to measure the photographic film’s sensitivity to light and referred to as film speed.

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 before being able to change the speed by loading a new roll that has a different speed. Usually, the speed you would choose is dependent on the subject you plan on shooting.

Without getting too technical how all this works on a digital sensor, you can take the basic concept introduced by photographic film 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, requiring more light, either through longer exposure time or a larger aperture.

The history of measuring film speed is long and complicated. The current ISO standard is, in fact, a combination of two older standards. Instead of boring you with the details, what you need to know is that you measure ISO using a linear arithmetic scale with “ISO 100” being the most common lowest value found in today’s cameras. Being a linear scale, “ISO 400” will double the amount of light from “ISO 200” and “ISO100” will half the amount of light. Some higher-end cameras do offer ISO values lower than “ISO 100”, either natively 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 the fact that in the digital age, 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 is going to 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, with larger crystals, or faster film, producing much more unsightly grain in the image. Many digital photographers try to replicate this grain structure during post-processing to try and emulate the film look.

The ugly part of digital sensors being able to increase sensitivity to light at will is digital noise. Noise, unlike grain on film, is very unsightly. It causes the loss of details and also affects the dynamic range of the sensor. All cameras handle noise differently, so if shooting in low light is something you plan on often doing, I would suggest looking 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 selectively.

Auto ISO

At the beginning of this article, I mentioned that when in either shutter or aperture priority, you will be responsible for setting the ISO and the corresponding component, and then your camera will determine the third component based on the exposure.

There may be times where all you care about is setting either you shutter speed or the aperture and then let the camera set both the ISO as well as the other component. 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 to prevent motion blur from either the subject or camera shake. The problem with this is that you will have to monitor your shutter speed to ensure it is fast enough and then adjust you ISO or aperture accordingly.

Auto ISO allows you to tell the camera your preferred ISO, which would generally be a low value. You will also tell it your minimum accepted shutter speed to avoid motion blur for the focal length of the lens you are using. The camera will then automatically set you preferred ISO value as long as the shutter speed remains equal to or higher than your minimum shutter speed. If the shutter speed starts to fall below your minimum value, the camera begins increasing the ISO to maintain that minimum shutter. It will also lower the ISO again once the shutter speed goes above the minimum.

Using auto ISO allows you to focus on your composition and the creative effect of your image as opposed to monitoring camera settings in a fast-paced environment where it might not be possible to take a second shot, like at a concert or a wedding.

Conclusion

So, understanding the exposure triangle requires you to first decide on your exposure value to ensure that you are correctly exposing for the current scene in front of you. Using your camera’s histogram is the best way of ensuring that you are exposing correctly.

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

  • Shutter speed controls how long the shutter is open and can be used 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.

Personally, when shooting, I tend to try and shoot at the lowest ISO setting possible so 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 or images of people.

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, like capturing wildlife or my kids playing.

Learning how to set your exposure and creative effects is one of the most basic and valuable skills that you will have to learn as a photographer. The key to mastering the exposure triangle is to go out and shoot with the intent to practice.

Over To You

Hopefully, this article has helped you to understand the exposure triangle if you are just starting in photography. If you want to know more about exposure, aperture, shutter speed, or ISO, let me know down in the comments below. Also, let me know how you use these components creatively in your images?

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One Response

  1. As someone who shoots a lot of landscapes, my 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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