Understanding the exposure triangle is by far the most important point to learn for someone who is beginning with photography. Of course this can be confusing initially but the essence of the triangle is light – you need the correct amount of light to correctly expose a picture. The Exposure Triangle covers the 3 ways (ISO, Shutter Speed, Aperture) that this can be achieved.
The Exposure Triangle
Aperture, shutter speed, and ISO make up the three sides of the exposure triangle. They work together to gather the amount of light needed for a correctly exposed photograph. If one variable changes, at least one of the others must also change to maintain the correct exposure.
A good place to begin is to talk about a stop of light. Understanding what a stop of light is, is key to getting the correct exposure. Below is a chart that shows how to increase the 3 key factors by 1 stop. Your camera may have other settings to the list below (e.g. f/3.5) and therefore this is to be used as a guide.
Each time you increase 1 stop, you double the amount of light going to the sensor. increasing the light will make the picture brighter and reducing by 1 stop will make the picture darker.
There is a correct amount of light that needs to go to the sensor to expose correctly and this depends on the conditions that you face. There is no perfect ratio to achieve perfect exposure.
So how do you add or take away a stop of light? To do this, we need to change the aperture, shutter speed, and/or ISO. Let us look at each of these individually.
Aperture refers to how far the shutter opens when taking a picture. The bigger the hole, the more light that reaches the sensor. In fact, each time you double the area of that opening, you double the amount of light or increase the exposure by one stop. On the other hand, if you half the area of the opening, you half the amount of light hitting the sensor. And you guessed it; that will decrease the exposure by one stop.
The smaller the F-Stop (the larger the shutter opens) the shallower the picture will appear. This is useful for portrait photography as it priorities the person and blurs the background.
The larger the F-Stop (the smaller the shutter opens) the greater the depth of field will be. This is good for landscape photography as the majority of the picture will be in focus. This is the first setting to review as it depends on the picture that you would like as to the setting that you’ll use.
Shutter Speed is the length of time light can hit the sensor. It is measured in seconds of parts there of. Shutter speed is probably the easiest of the exposure triangle sides to understand. To double the amount of light, we need to double the length of the exposure. For example, moving from a shutter speed of 1⁄60 s to 1⁄30 s will add a stop of light because the shutter will remain open twice as long. Changing from a shutter speed of 1s to 1/8 s will decrease the exposure by three stops. Why? From 1s to 1⁄2 s is one stop. Then 1⁄2 s to 1⁄4 s is another stop. Finally, 1⁄4 s to 1⁄8 s is a further halving of the time the shutter remains open or the third stop.
This is my go to setting to get the picture that I want. I typically take landscape shots and can use my tripod if needed. I have to play with the other settings if the picture involves anything that moves!
The final variable in the exposure triangle is ISO. You can think of ISO as the sensitivity of the digital sensor. The higher the ISO value means that the sensor works harder to get the picture. Low ISO values mean that the sensor will have to rely on Aperture and Shutter speed to make the correct exposure.
Below is the ISO scale. As with shutter speed, this should be easy to understand! Doubling the ISO equates to a one stop increase in exposure. Halving the ISO leads to a reduction of the exposure by one stop.
Increasing the ISO leads to noise (grainy effect on the picture). This is why the ISO should be the last resort to achieve the picture that you would like.
A stop is the doubling or halving of the light that makes up an exposure. We can add or subtract stops by changing the aperture, shutter speed, or ISO. Now you’ll be able to increase your exposure by a couple of stops to achieve the correct exposure.
I hope you found this article useful!