I have to admit one of the toughest parts of starting out in digital photography for me was understanding the exposure triangle. The exposure triangle shows the relationship between aperture, shutter speed, and ISO settings on your camera. These are the three things that affect the exposure of your image. I know most people just go with the Auto setting when they buy a shiny new DSLR camera and let the camera decide the settings. The problem with that is that although cameras are pretty smart, they still can get it wrong. If you really want to take artistic control of your photos and not just shoot snapshots in Auto mode, you have to understand the exposure triangle. Luckily, you don’t have to know all the higher-level math behind the settings. If you are like me, you just want to know what each of them does and how one affects the other, right?
Well, I’m going to get down to just what you need to know about the exposure triangle so you can get out and shoot with your camera, not make you sit through a math lecture to show you how smart I am. It’s enough to know that once you get off of Auto mode any time you change one of these things it affects the other two. They have to be adjusted to create a proper exposure. Let’s begin by going over each setting and how they affect your final image.
The first setting in the exposure triangle is the aperture setting. Aperture refers to the opening formed by the blades in the lens that determines the amount of light hitting the camera sensor. This is what is referred to as the f-stop number. As you can see from the graphic, higher numbers mean a smaller diameter hole for light to travel through. Lower numbers mean more light hitting the image sensor in the camera. Changing the aperture setting from, for example, f4 to f5.6 means double the amount of light hitting the image sensor. The aperture also controls the focal plane in the image. With a smaller aperture like f16 or even f22, the image will be in focus from very close to infinity. When you open the aperture wide, you narrow the focal plane. This is how you take photos with the subject in focus and the background blurry. I covered depth of field in more detail in a previous post.
If you shoot in aperture priority mode, you set the aperture and the camera will then adjust the shutter speed according to what the internal meter thinks is a proper exposure given the ISO you have set. Many times the camera gets it right, but sometimes the camera will underexpose or overexpose your subject. That’s why learning the exposure triangle is so important. When you understand how it works you can shoot in full manual mode to achieve the creative look you want. However, for many shots aperture priority will do a good job for you, and thinking about setting the shutter speed is one less thing you will have to worry about.
Shutter speed refers to the amount of time the shutter is open and allowing light to strike the image sensor. Fast shutter speeds freeze action. Slower shutter speeds can smooth out running water or help with gathering enough light in night photography. Below are examples of a fast shutter speed and a slow shutter speed.
As you can see, shutter speed can help you creatively in creating an image. But in the exposure triangle, you need to be aware that you need to adjust your aperture when you change your shutter speed. The other option is to change the camera setting to use shutter priority and let the camera adjust the aperture for you.
ISO stands for International Organization of Standardization. This designation has carried over to digital photography from film, where the film speed referred to the light sensitivity of the film. Now ISO refers to the sensitivity of the digital sensor to light. Higher settings mean the sensor is more sensitive to light. There is a tradeoff, however. Digital sensors can also have noise induced by adding sensitivity. Typical DSLR cameras have the ability to set ISO from as low as 50 to 12,800 or higher. Unfortunately, as stated, a higher ISO setting will introduce grain and noise into your image. It’s best to experiment and see the maximum ISO setting your camera will allow and still produce an acceptable image. That way you will know the limits of your camera when it becomes necessary to increase your ISO.
Putting it all together
Now that you know what each leg of the exposure triangle is and how it affects exposure, you can start working with different settings creatively. For instance, let’s say you are shooting a model indoors with studio flash. You want to open up your aperture so you have a blurred background to accentuate the model. You know from understanding depth of field you need a wide-open aperture. You also know opening up your aperture will let in more light, so you have to either set a faster shutter speed to compensate or set a lower ISO to make your camera sensor less sensitive.
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Check out more great photography tips on our Photography Tips & Tricks page.