Introduction
Photography is a fun way for families to remember birthday parties, graduations, and vacations. But if you treat photography as a serious hobby or profession, you expect more from the images you create. That’s why you need to know how to make the perfect exposure. And the basis of a great photo is an understanding of the elements of the exposure triangle. There are three key parts to the exposure system of a camera, so putting them in the form of a triangle makes a simple symbol for visual reference. Let’s look at it from all three angles.
Table of Contents
What is the Exposure Triangle?
Using a camera on the Auto setting means the camera does all the thinking for you. The Auto option balances all the factors of the exposure triangle without any extra help. Light is captured by the camera in three ways: it comes through the aperture, which is the opening of the lens; it passes the shutter for a brief amount of time, which is the shutter speed; and the sensor is set to a specific sensitivity, which is called ISO. When you use these areas in the correct combination, you have a result that is not too bright and not too dark.
However, if you switch the camera to Manual mode and change a setting on the aperture, shutter speed, or ISO, it will impact the exposure, so you will have to make another adjustment to one or two of the others to balance it out again.
Why would you want to change to Manual mode? The Auto option on a camera produces a photo using an even amount of light from the aperture, shutter speed, and ISO to give a well-balanced photo. But if you want to take full control of your camera’s settings to be more creative, you have to know how to juggle all the sections of the exposure triangle to make them work in harmony with each other.
To a lesser degree, switching to Program mode, Aperture Priority, or Shutter Priority mode (sometimes called Time Value) means you can produce different effects by choosing to change one element of the exposure triangle. The adjustment won’t compromise the exposure in those settings because the camera automatically changes the other factors to balance the shot.
Understanding what is going to happen when you change one of those elements is an important part of photography, so let’s explore each ‘side’ of the exposure triangle.
The Elements of Exposure
Aperture: On most cameras the opening in the lens that lets in the light is changeable. When you increase the size of the opening, you let more light through to the film or digital sensor. When you make the opening smaller, less light gets in. Obviously, you get a brighter photo with more light, and less light gives you a darker image. This explains why the aperture is an important part of the exposure triangle, but the size of the aperture also affects the type of image being created. Aperture controls the depth of clarity within a scene.
Aperture Settings Don’t Just Impact Exposure: Depth of field is the term that describes how much of a photo is in focus, and it’s the result of the size of the aperture. A big opening of the aperture creates a lot of blur around the area you have focused on.
Imagine you are meeting a girlfriend at a cafe. When you arrive, you see that she has chosen a table in the sun, and as she sips her coffee she is deep in thought. Before she notices that you have arrived, you realize it could be a fantastic opportunity for a lovely, candid photo. So you take out your camera and take a photo on Auto mode. But it’s a disaster! Behind your friend, there are so many people that it’s distracting, and the graffiti on the wall nearby is ugly.
Don’t ask her to move. She won’t have that same natural and thoughtful expression that you wanted for your shot. You can change this scene by adjusting the aperture setting. Switch to Aperture Priority or Manual mode and open the lens to a wide aperture such as f/2 before focusing on your friend’s face. This time when you review the image on your screen you’ll find that her face is clear and sharp, but the foreground and background are out of focus. The wide aperture produced a shallow field depth, highlighting your subject and removing the distracting elements around her.
Changing the aperture to a small opening gives the opposite result. Sometimes you want to have clarity throughout the image. For example, in landscape photography, you want to see the wildflowers in the foreground, the peaceful lake in the middle of the frame, and the snow-covered Alps in the distance. And you want to see the detail in all of them.
Using an opening that is half the size of the aperture makes another type of shot possible. In this case, your subject stays in focus, while the foreground and background have a subtle blur. Because the people or objects you have focused on are sharp, your eyes are immediately taken to them, but you will still notice features in the background that give context to the environment around the subjects. Changing the depth of field is a powerful way to add creativity to your composition.
Shutter Speed: Deep inside your digital camera there is a barrier between the lens and the sensor. This shutter opens and closes for a designated amount of time, allowing the light to form an image on the sensor. If you are shooting on a bright day and choose a fast shutter speed to reduce the amount of light hitting the sensor, then you won’t overexpose the image. Or, if you find yourself in dim lighting, use a slow shutter speed to allow extra light onto the sensor, and then you won’t underexpose the photo.
Shutter Speed Settings Don’t Just Impact Exposure: A good way to make your photos stand out from the crowd is to use shutter speeds to suggest movement, or to freeze a moment in time. A fast shutter speed makes an image that has exactly the right amount of sharpness in action shots. Or you can deliberately choose a slow shutter speed to show motion-blur on waterfalls and the wheels of racing cars.
ISO: In the days when film cameras were popular, photographers used 100 ASA film when it was a sunny day, 200 ASA when it was slightly overcast, 400 ASA in fully overcast conditions, and 800 ASA for shots in low light. Low-speed films needed bright conditions to get the best results, whereas high-speed films were more sensitive and could take photos in dim situations. High-speed films used large grains of silver halide to capture the light, so the disadvantage was that photos looked grainy.
Digital cameras don’t use film, but their sensors react in a similar way to the sensitivity of film. A sensor’s sensitivity to light is known as its ISO. The lower the ISO, the less sensitive it is to light, so you need bright conditions to capture an image. A high ISO is more sensitive, so it does not need as much light to make a good exposure.
ISO Settings Don’t Just Impact Exposure: Using low ISO in bright conditions produces a photo with fine detail. When you set the camera to high ISO, it makes a grainy image similar to a photo that is shot on 800 ASA film. In digital terms, we say that the photo has a lot of electronic noise.
Understanding Exposure Via a Metaphor
Here’s a metaphor showing how the exposure triangle works. In this analogy, we’re swapping light for the water. Use your imagination and think of a garden hose filling up a large birdbath. Aperture relates to the width of the hose, ISO is equivalent to the pressure of the water, and shutter speed is the amount of time that you allow water to flow through the hose.
If you want to fill up the birdbath in a steady manner, then you would use a standard gauge hose, a steady amount of flow, and it would only take about a minute of your time. If you use a wider hose, or you have more water pressure, or you let the water run for too long, you will have too much water for the birdbath and it will splash everywhere. This is similar to an overexposed image. And if you use a hose with a small diameter, or you turn down the water pressure, or you don’t let it run for very long, you won’t have enough water for the birds. This is equivalent to an underexposed photo.
However, you can adjust the settings and still get a balanced amount of water by juggling these variables. You will still get a good result (a full birdbath) with a narrow hose as long as you increase the water pressure, or let it run for longer. Or you could choose to use high pressure with a wide hose, but only let it run for a very short amount of time.
There are so many possibilities, which is great because that’s what happens when you take photos. You may want a fast shutter speed to capture the action, but if you don’t have much light then you have to open the aperture more than usual. Or you may want to have a wide aperture to blur out the background, but it’s a bright day, so to avoid overexposure you have to use a fast shutter speed to cut down on the amount of light reaching the sensor. Another common situation is photographing in low light, which normally means you need a slow shutter speed to allow more light to the sensor, but you could get blurred results from camera movement, so you have to bump up the ISO in order to use faster shutter speeds. It’s a balancing act, but it’s fun when you get the hang of it.
Measuring Aperture, Shutter Speed, and ISO
The aperture of a lens can be set really small, very wide, or anything between. This opening is called the f-stop, which relates to the ratio of the opening to the focal length of the lens. Every time you adjust the f-stop in one direction or the other, you double or halve the intensity of light hitting the sensor.
On a digital camera, shutter speed is the amount of time that light moves through the aperture and lands on the sensor. This is measured in seconds and fractions of a second. If your intention is to take a photo of city lights, set your camera on a tripod and open the shutter for about 10 seconds. But if you want to take an action shot of football players having a match on a sunny day, choose a high shutter speed like 1,000th of a second.
Each time you decrease the shutter speed by one unit on the dial, you double the length of the time the shutter stays open. For example, in the middle of the scale, you can jump from 1/250th second to 1/125th of a second and you double the amount of light hitting the sensor. Going the other way from 1/250th of a second to 1/500th of a second means you halve the amount of time that light is available to the sensor.
ISO is measured in numbers similar to film speed. There are familiar units such as 100, 200, and 400, but on a digital camera, they can go all the way to extremes such as 32,000 ISO. Each time you increase from one ISO unit to the next you are doubling the amount of light available to the sensor. Decreasing from one speed to the next one down means you make it darker by one-stop
Wrapping It Up: The Exposure Triangle Explained
The exposure triangle may seem confusing at first, but when you have a good understanding of it you’ll find that camera settings make more sense. Photography becomes easier when you know the basic principles and have a better idea of what you need to do to make a good exposure. Maintaining a good exposure while changing the depth of field, capturing action with faster shutter speeds, or deliberately increasing or reducing electronic noise gives you control over your images. Instead of being someone who takes snapshots, it turns you into a photographer!
