Learn Photography: ExposureTriangle - CB Friedland

The pieces are in place. It is time to explain how ISO, Shutter Speed, and Aperture interact together to create properly exposed images. Once you understand these concepts, using automatic mode will be a thing of the past. ~CB


Learn Photography: ExposureTriangle

Previously, ISO, Shutter Speed, and Aperture we discussed in isolation. It is now time to work through an example that will bring them all together.

Why an Exposure Triangle?

The settings that will yield a proper exposure is what is determined by the Exposure Triangle. Why a triangle? Very much like a triangle, the three elements that get you to proper exposure, are all dependent on each other.

Grab a piece of paper, and draw two sides of a triangle. What do you notice? How you have drawn the first two lines, predetermines what the length and angles of the third aspect of the triangle will be.

Remember, when we are talking about exposure, we are talking about the light in our images. ISO, Shutter Speed, and Aperture all impact the amount of light that enters your camera and how your sensor reacts to it. Because we have the option to change multiple settings at once, there are several different combinations of ISO, Shutter Speed, and Aperture that will provide proper exposure in your image.

We Set Our Shutter Speed

Let’s dig into this a bit deeper with an example. Let’s consider a situation where you are shooting a fast-action scene, say a football game either at night or indoors. With most sports photography, the goal is to freeze the action, capturing a critical moment in the match. We know that shutter speed is crucial to freeze the action, and at a minimum 1/1000 of second is needed given the pace of the game. We just drew the first side of the triangle.

Determine the Second Side of the Exposure Triangle

Now let’s work on the other sides of the triangle. With this fast shutter speed, the shutter is open for only a brief moment. Not much light gets sent to the sensor. The player’s movement will be frozen, but it doesn’t give the sensor much time to capture the image, especially since we are shooting in low-level light conditions (at night or indoors).

To compensate for this, we will have to adjust the Aperture and ISO accordingly. Let’s start with Aperture. The fast shutter speed has restricted the light hitting the sensor. One way to provide more light to the sensor during that brief moment the shutter is open is to make the opening the light comes through wider.

What Effect will Aperture Have?

We learned that at smaller Aperture settings (the lower numbers) the opening that allows light into the sensor is wider (larger). But what else did we learn about Aperture? What effect does it have on the amount of detail in the background of your image, or more technically, the depth of field in the picture? The smaller the aperture number, (the larger the opening), the less detail captured in the background of your image. The depth of field around your subject also gets smaller at each lower Aperture number.

There is a certain amount of depth of field that is necessary to tell the story or capture the critical moment of the game. For example, take a game-winning touchdown catch. You want the receiver, the ball, and any immediate defenders in tack sharp focus. These are the things directly involved in the determining play. But what about other players not involved in the catch? What about the fans? Does it matter if they are in focus if they are not part of the story you are trying to tell? Not likely.

What I am getting at is that there will be a certain depth of field you will need to capture the moment, and this will determine the minimum Aperture setting you will be able to use. We just drew the second side to our triangle. What I am getting at is that there will be a certain depth of field you will need to capture the moment, and this will determine the minimum Aperture setting you will be able to use. We just drew the second side to our triangle.

Determine the Third Side of the Exposure Triangle

In a perfect world, the adjustment in Aperture will allow enough light into the camera to support the Shutter Speed, without any change needed in the camera’s ISO. Given that in our example we are shooting in a low-level light condition, this is not likely, however.

The light entering into the camera will not be sufficient to allow the sensor to capture the image with proper exposure, and the image will be too dark. In our discussion on ISO, we talked about how with each increase in the ISO setting, your camera’s sensor becomes twice as sensitive to light, allowing it to capture the light hitting it faster.

As we learned, this comes at a cost, however, as “noise” gets introduced into your images (especially in the dark tones and shadows) causing it to become grainy or pixelated and losing tack sharp focus.

Adjust Your ISO to get Proper Exposure

Returning to the triangle, we have drawn two sides of it, so the third side (in this case, the ISO setting) also has been determined. The quick answer is we now need to set the ISO to the lowest setting that will allow the sensor to process the light fast enough for proper exposure.

You can achieve this can by taking multiple test images before the game at different ISO settings and comparing the level of light in each. This works well for instance where the light levels do not vary by much.

Here is a tip for cases where the light does change. It isn’t uncommon for there to be differences in lighting on a player, in different parts of the field, and, we will encounter situations where the ISO will need to be adjusted. Changing the ISO settings on our cameras is not necessarily a quick setting change, like changing Shutter Speed or Aperture. Because of this, there is the potential to miss “the shot.”

In these cases, setting ISO to Automatic makes sense. Your camera will adapt to the lighting on the player as he moves across the field as necessary, allowing you to focus on pressing your shutter at the decisive moment.

My Challenge to You

1.  I would like you to take your camera and replicate the example above. You don’t need to go to a football game, just the situation of action in low-light. Now do the opposite scenario.

2.  Determine your required Depth of Field or Aperture first. Then reason through the rest of the triangle. Keep doing this until it becomes instinctive.

Wrapping it Up!

That is the Exposure Triangle in a nutshell. We have gone through only one of the many scenarios that you will encounter while shooting. Your Challenge work will expose you to others.

The important thing to remember when thinking about the exposure triangle what your settings should be is to think about the final image that you would like to create. What depth of field do you need? Is it ok if portions of the photo are blurry? Are you going for a darker, moodier image or a bright ethereal look? Figuring these things out first will lead you to the settings that you need.

Use the fact that you can obtain proper exposure with multiple combinations of settings to your advantage.

Experiment… See what works, and more importantly, what doesn’t work. Find all of the combinations that lead to a properly exposed image. See which one satisfies the story you want to tell.

As always, if there are any questions or comments you might have about today’s post, please add them to the comment section below, or you can email me. You can also find me on Facebook,  and Instagram.

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