When you take a picture, you control how much light enters the camera. Let too much light in and you’ll overexpose your image, making it too bright. But, if you don’t let enough light in, you’ll underexpose your image, making it too dark.
The ‘exposure triangle’ is an important balance between shutter speed, aperture and ISO. Each has a different role to play, but they play very well together.
Shutter speed – controls the length of time that light enters your camera
Aperture – controls how much light enters your camera
ISO – controls how sensitive your camera is to light
When you take a photograph, your camera’s shutter opens, letting in light. It stays open for a period of time and then closes, cutting off the light. For example, when it’s darker you have to use slower shutter speeds and when it’s brighter you have to use faster shutter speeds. This is because the shutter speed controls the length of time light enters the camera.
Aperture can to control the amount of light that enters your camera. This is measured by the ‘f-stops’ on your lense. All lenses vary but the ‘f-stops’ can range from f/2.8 (more light in) – f/22 (less light in).
The aperture setting will also change the shutter speed – for example, in f/22 the shutter speed is slower (as you’re allowing less light in).
When it’s dark you need to make the most of the limited light, so you can increase the sensitivity of your camera by increasing your ISO. When it’s bright, you can decrease the ISO.
Every time one of these factors is changing the exposure is affected. Depending on the type of photography you do and the result you want to achieve you can changer accordingly your settings. For instance if you shoot sports photography then you need a faster shutter speed to freeze the motion. On the other hand if you shoot music photography you might need to push your ISO higher or open your aperture more.
In the following example my “perfect” exposure is at ISO 1600, 1/200th of a second shutter speed and aperture f/5.6. I wanted to get a bit more shallow depth of field. I changed my F stop to 2.8 which means I changed the aperture value by 2 full stops. Since I let more light my image will be overexposed.(image 2,3)
In order to compensate for this and keep my exposure triangle in balance I need to change either my ISO or my shutter speed. Any changes should be by 2 steps. My ISO was 1600 so I need to set it to 400.(image 5). If I choose to change the shutter speed then I should set it to 1/800th.(image 4)
I can also compensate for the change of aperture by changing one step both ISO and shutter speed. The exposure triangle will be again in balance and it’ll give me the same exposure. (image 6)
The exposure triangle is probably the most important step to get out of the auto mode and start being creative. Grab your camera and try the exact same procedure and see yourself how the exposure changes.