Understanding the Exposure Triangle
Understanding the purpose and value of exposure is an essential skill set to have as a photographer, and it's determined by three camera settings: aperture, shutter speed, and ISO, also known as the Exposure Triangle. Here's everything you need to know about controlling exposure.
What is the Exposure?
Exposure is how an image is recorded by a camera sensor and how much light is captured. It determines what the image you capture will look like.
Underexposed – Underexposure is the result when not enough light hits the film strip or camera sensor.
Overexposed – Overexposure is the result when too much light is hitting the camera sensor or film strip.
What is the “Correct” Exposure?
When nothing is blown out (highlights) or lost in shadow in an image, it is correctly exposed.
What is the Exposure Triangle?
The exposure triangle is the relationship between your aperture, shutter speed, and ISO to regulate the amount of light that goes into your camera.
Aperture
Your aperture, or f-stop number controls how much light can pass through the lens of your camera at a particular shutter speed. A smaller aperture will let less light in than a larger one. The higher the f-number, the smaller the aperture. The lower the f-number, the larger the aperture.
Shutter Speed
The shutter speed determines how long the sensor is exposed to light and is measured in seconds or fractions of seconds. If you double the shutter speed, your sensor is exposed to light, half as long, and therefore, it's 1-stop less. If you lengthen the time it's open by twice as long, you increase the overall exposure 1-stop of light.
ISO
Stops of light in terms of ISO are straight forward. Double the ISO, and you have double the amount of light sensitivity and therefore, 1-stop of light.
Stops of Light
A stop is a doubling or halving of the amount of light let in when taking a photo. For example, if a photographer says he's going to increase his exposure by one stop, he's going to capture twice as much light as on the previous shot.
Putting it All Together
Let’s say your camera settings are f/8, 1/60, ISO 200 and you wanted to open up your aperture to f/2.8 for a shallower depth of field. To keep the SAME level of overall brightness (exposure), you could change your shutter speed to 1 /500 (or -3EV) to compensate for that change. Alternatively, you could change your ISO to 100 and your shutter speed to 1/250 (f/2.8, 1/250, ISO 100) for the level of overall brightness.
For example, the following settings would produce the same level of overall brightness in the image:
f/8, 1/250, ISO 400
f/4, 1/500, ISO 200
f/16, 1/30, ISO 200
To Make Things Even Easier to Remember
A stop of light is double or half the amount of light in regards to the overall exposure of an image.
Doubling your shutter speed will DECREASE your overall exposure 1-Stop.
Doubling your aperture will DECREASE your overall exposure 1-Stop.
Doubling your ISO will INCREASE your overall exposure 1-Stop.