The Exposure Triangle in Photography

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Why is the exposure triangle so important to creative photography? Well, without it there is no creativity to your photography which makes it really important. Oh, you don’t know what the exposure triangle is? It’s your three most fundamental keys in photography. Aperture, shutter speed and ISO which together control how much light reaches your sensor.

In order to understand the exposure we need to look at each of them individually. But before we do that, a little something on the side. On the mode dial of your camera where you see the symbols A(v) S M P or Adep there is also a little green square which represents automatic. This is a no no if you want to become a creative photographer. Automatic means that the camera chooses the setting for you and you just point and shoot. Those symbols represent what we call the creative modes. The other little pictures are the idiot modes which we don’t use either.

So let’s take a look at the three modes of the exposure triangle.

aperture

“Face the World” captured by Abbas Khan (Click Image to See More From Abbas Khan)

1. Aperture

Aperture controls how much light reaches the sensor. To me the aperture setting is the most important of the three because it allows you to control depth of field or as I like to call it, depth of focus. This allows you to set how much of your image will be in focus.

A shallow depth of field is when on a portrait the background is beautifully blurred out with only the person’s face in focus. This gives a lovely image image as the background clutter is blurred into an abstract milky kaleidoscope of soft colour.¬†In order to achieve this a small aperture number or f-stop is used.

Whether the aperture is large or small is immaterial, what you need to remember is that a small f-stop (such as f/2.8) gives you a small or shallow depth of focus, i.e. only a small portion of the image is in focus as you see in a portrait of a person.

To achieve a large depth of focus you do the opposite by using a large f-stop number (such as f/22), i.e. a large portion of the image is in focus as you often see in a landscape photo. This mode is important with creative photography as it allows you to control what is in focus or out of focus. What you also need to know about aperture numbers or f-stops is that a small number lets in a lot of light and a big number lets in a little light. Remember this. Most times I will shoot on the A(Nikon) or Av(Canon) mode as this gives me control of the aperture while the camera selects the shutter speed.

2. Shutter speed

Shutter speed controls the length of time the shutter is open. This allows you to control the sharpness of the image. An action photo needs a fast shutter speed in order to freeze the shot. But if you want it blurred to simulate speed then a slower speed will achieve that level of creativity.

shutterspeed

“Electric Dreams” captured by Jet Rabe (Click Image to See More From Jet Rabe)

When shooting on the S mode the camera will control the aperture while you choose the shutter speed. What you need to remember is that a fast shutter speed i.e. 1/125 to 1/1000th of a second lets in a little light and a slow speed lets in a lot of light.

3. ISO

iso

“Puddle” captured by Andrew Scott (Click Image to See More From Andrew Scott)

This is really simple as it controls the sensitivity of the sensor and is a last resort when you can’t let in sufficient light with the aperture or shutter speed settings. There are times when you can’t select use a wider aperture as this will make the depth of field to shallow so it’s necessary to increase the ISO level. The same goes for the shutter speed. The downside is that the higher the ISO the more noisy the image.

Now, how does the exposure triangle work? There are times when you want to take a shot of a wind surfer twisting through the air. This means you need a fairly fast shutter speed. Because he is moving a shallow depth of field won’t work as part the surfer may be out of focus so you need a large f-stop number. If you remember, a large f-stop number means less light and a fast shutter speed also means less light. So you have a problem.

The important thing here is that you want a fast shutter speed to freeze the fast action. You can do one of three things. Slow down the shutter speed which won’t work as you need to freeze the frame. Secondly, you can increase the amount of light by choosing a smaller aperture f-stop number. This won’t work as only a small portion of the image will be in focus. The only thing left to is to increase the sensitivity of the sensor to the available light by increasing the ISO level. This lightens the image and allows your fast shutter speed and large depth of field.

The way exposure triangle works is that it if you change one of the three settings it will affect the others. I must emphasize here that the exposure triangle is most effective when using the manual mode so you have full control of all three settings. By being aware of these three aspects of your photography you will be able to increase your creativity. Happy shooting!

About the Author:
Wayne Turner has been teaching photography for 25 years and has written three books on photography. He has produced 21 Steps to Perfect Photos; a program of learner-based training using outcomes based education.

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7 Comments

  1. Dan says:

    How does changing ISO affects sensor sensitivity? Changing ISO amplifies the light captured by the analogue sensor device. Hence the increased noise levels.

  2. Jacques says:

    ISO is the sensitivity to light, at least that is how it has always been explained to me and a lot of others over the years. So that is how it affects the sensor sensitivity, unless the guys that have explained it are wrong.

  3. Wayne Turner says:

    As you increase the ISO 100-3200 it increases the sensor’s sensitivity to light. It works in basically the same way your aperture when it is opened up wider and lets in more light. When you slow down the shutter speed it does the same thing by allowing more light to reach your sensor. As you adjust one it affects the other two, hence the aperture triangle.

  4. David says:

    Sensor sensitivity is a confusing issue. Let me throw-in my two cents. Think of it this way: a sensor is made up of millions of solar cells (like the ones on our roofs). When light (from our cameras) hit the solar cells they produce an electrical current. The more light the more current. This is fixed by the physical properties of of the solar cells. You (the camera operator) can not change the sensitivity of the solar cells In other words, you can not get more current out of the same amount of light.

    What happens is when there is not enough current (light) to produce an adequate.exposure, raising the ISO amplifies the voltage produce by the cell, thus increasing exposure. This is done downstream from sensor and is why more noise is produced as ISO is increased Same anology as film.

    Arguing whether the senstivity of the sensor is increased by raising the ISO is moot (or silly). We all know what is meant. If one needs more exposure, increase the ISO which will increase the sensor’s (systems) sensitivity to light.

  5. Punk Toad says:

    Do you have any advise for point-and-shoots that only allow control over ISO but no direct control over A & S? Do you have thought to share on D-Lighting and HDR composite rendering?

  6. Wayne Turner says:

    Unfortunately the exposure triangle can only be controlled effectively if you have control over aperture and shutter speed. The nearest you can get to achieving this on a point and shoot is by using the head on your controls which is for portrait and gives a shallow depth of field and the other is the landscape which gives you a large depth of field. The little man running gives a fast shutter speed. Besides this there isn’t much you can do with an automatic point and shoot.

  7. Crystal Carrie says:

    Its amazing what a camera could make you see

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