Exposure Triangle – A Triangle that Catches Light

Exposure Triangle – A Triangle that Catches Light

When the camera captures an image, that means the sensor or film is exposed to the light and records the light. In this process, how the light is recorded will determinate how the image or photo look like. Normally, the more the light is recorded, the brighter the image, and vice versa. In photography, no matter film or digital, there is a range from the brightest to the darkest. Each camera have different range, this range is called “dynamic range“. If the light recorded is more than the dynamic range can present, that part will become totally white. Conversely, if the light recorded is less than the dynamic range can show, that part will become totally black. This is where clipping occur. There are always three components which make the “exposure”. They are aperture, shutter speed and ISO sensitivity. These three elements are called “exposure triangle”.

What is the Exposure Triangle

Exposure TrianglePhotographers use different settings of these three parameters to control exposure. The most difficult skill is to determine when to make changes to which element. Should I increase the ISO sensitivity? Should I use a smaller aperture or should I use a slower shutter speed? Let’s use a simple diagram to explain.
Aperture: Control how much light enters the camera.
Shutter Speed: Control how long light can enter the camera.
ISO Sensitivity: Control how sensitive the camera reacts to light.

Is this still too complicated? Let me use an example of collecting rain water to elaborate. Imagine you are collecting rain water by some buckets. You cannot control how big the rain is. That is similar to that you cannot control the light in the environment. The size of the bucket represents aperture, which let more water to enter the bucket at the same time. How long you put the bucket in rain represent the shutter speed, which is how long you open the door of camera to let the light in. How many buckets do you use represents the ISO sensitivity, the more buckets you use, the more sensitive does the camera react to light.

This is a pretty simple concept. A photographer’s job is to ensure the correct among of light goes into the camera. If too much light go into the camera, the image will be overexposed. It is just like the bucket fill with too much rain water. If there is too little light goes into it, underexposure occurs. That is the same as you collect too little rain water. When you familiarise with the exposure triangle, you can create image with exposure that you want. Let’s discuss each item in more detail.

Aperture Size

Aperture size is the first parameter of the exposure triangle. The aperture size is used to control how much light enter to the camera in the same shutter speed. It also controls the depth of field. I will discuss about depth of field in more detail in the later section.
f-stop compare
Aperture size represents in a ratio number, for example, 1:2.8 or f2.8. This is representing the ratio of focal length and the actual size of aperture. There is only one thing that you need to remember, the smaller the number, the larger the aperture. Normally the largest aperture for a zoom lens is f2.8 while f1.4 for a prime lens.

Shutter Speed

Some photographers may say exposure time instead of shutter speed. Actually they are the same. Shutter speed is the time that camera allow light to go in. It plays an important role in the sharpness of the whole image. When you use a longer exposure time, the probability of occurrence of vibration would increase. Also, if you are capturing moving object, slower shutter speed would result a blur image due to the subject movement. A good tripod is needed if you want to use extremely slow shutter speed to create special effects. For example, you may need 1/1000 or faster to capture sport or animals. To create nice light painting or the light track of vehicles, you may need a few second or longer. Here is an example of shooting a fast moving object, a fan, with different shutter speed. Pay attention to the blades movement.

shutter speed compare

ISO Sensitivity

ISO is the last parameter in the exposure triangle. It was hard to change the ISO in the old days because each roll of film has fixed ISO. However, thanks to the technology, photographers can now choose different ISO sensitivity. For the same aperture and shutter speed, a higher ISO results in a brighter image. I usually use a higher ISO to reach a faster shutter speed so that I can take images without handshaking. However, a higher ISO will lead to more noise, which lowers image quality.

ISO compare

Most of the time, photographers want ISO as low as possible, ISO100 is the lowest for most cameras, but due to some environment constraints, higher ISO is required to take the picture. Modern full frame cameras can produce great smooth images even under ISO3200. Most of the top models, such as Nikon D4 and Canon 1Dx, can produce smooth usable image even under ISO12800. That is one of the reasons why they are so expensive.

Arranging Correct Combination

I think you get the concept of the essential elements in exposure triangle, but how to arrange the combination in order to get the correct exposure? It is important to know that human eye is a powerful organ which automatically adjusts the brightness to different environments. It means that except extreme bright or dark, naked eye is not sensitive enough to the amount of light in the environment. Experienced photographers normally used to memorize the value of setting of different environment in the old days. In digital world, memory is so cheap that we can have unlimited trial and error until you get the exposure you want. If you do not have enough time to do “ try and error” or you want a faster way to get those value, you can use semi-auto mode. In the last post, the camera mode, I have already given some introductions of making “correct” value of the exposure triangle. While taking picture, aperture-priority and shutter-priority modes are most often used. Steps are as below.

  1. Think about which perimeter you want to control, the depth of field or shutter speed?
  2. Choose the corresponding mode. Choose aperture-priority mode if you want to control the depth and choose shutter-priority mode if you want to control the shutter speed.
  3. Set ISO sensitivity, the lower, the better. In this step you need to consider if you need to boost up the ISO to achieve better shutter speed to prevent handshaking or motion blur. You may consider to use auto ISO sensitivity.
  4. Press the shutter.

By following the above steps, you should come out with a normal exposure photo in most cases. Sometimes you may feel the photo is too bright or too dark. In this case you may need to reset the exposure compensation.

Exposure Compensation

exposure compensationExposure compensation is used to tell the camera to let more or less light to come in by comparing to normal situation. You can find a button which shows +/- on the camera. That is the exposure compensation setting. When it is set to positive, say +0.7, the image will be 0.7 stop brighter, and vice versa. As the camera is using the reflection light metering method to calculate the correct exposure value, black and white subject will easily affect the metering. Please remember this: “+ for white, – for black”. In other words, when you are shooting white things, such as snow mountain, please allow some positive compensation. Use +0.7 as first try. If the result is too bright, then decrease the compensation until you satisfy. You should use negative value for black objects. Besides, you can make some positive compensation if you want the image brighter, i.e. whiter. So, please remember “+ for white, – for black”. Below is the result of setting exposure compensation to different level.

The exposure triangle is such an important topic in photography. I hope this post explains each of parameters to you clearly. Feel free to leave a comment if you get stuck or have other questions. Please do me a favour by clicking the sharing button down below to share my post to your friends. It helps me a lot and of cause helps your friends too.