This trifecta is also known as “the exposure triangle,” and understanding how the elements work by themselves and together will allow you to better predict the outcome of a photo. Using the manual settings on your camera gives you control over these settings, and becoming familiar with them is the first step to better photographs. Let’s break each element down further.
Refers to how sensitive the camera’s image sensors are to light. Generally speaking, the lower the cameras ISO setting the less sensitive it is to light; the higher the ISO setting the more sensitive it is to light.
You will want to use a lower ISO setting for shots in brightly lit places, such as sunny days outdoors. And conversely, you’ll use a higher ISO setting for shots in dimly lit places, like a restaurant or concert.
One thing to remember is that shooting with a high ISO setting increases the noise in the photo (tiny, grainy specs that appear throughout the picture). Depending on the photo, you can compensate for a higher ISO by increasing aperture and shutter speed (this does not apply to all scenarios though, such as shooting without a tripod).
From the folks at Digital Photography School, above is a comparison shot of two images taken at different ISO settings. The flower on the left was shot at an ISO of 100, and the flower on the right was shot at an ISO of 3200. Notice that the high ISO shot is both brighter and more colorful, but has more noise (graininess) than the low ISO shot.
Refers to the size of the lens opening, which controls how much light is allowed to enter the lens. The larger the opening the more light is let in, the smaller the opening the less light.
Now for something a little less straightforward, aperture is measured in f-stops (f/number) where the smaller the f-stop the larger the aperture, and vice versa. So f/4 (large aperture) lets in more light than f/22 (small aperture). Personally, this caused me a good deal of confusion, but practicing and playing with the settings helps you get used to this.
Aperture also helps to control depth of field (DOF), which is the area in a photo that is sharp and in focus. You’ve seen photos like this, where one element will be in sharp and crisp (such as a bug on a leaf), and the rest of the photo is blurry. Generally a higher f/stop (smaller aperture) means a larger depth of field, in which more elements of the image will be in focus. A lower f/stop (higher aperture) means a more shallow depth of field, with some areas in sharp focus and others not.
Here’s something that helped me remember: big number equals larger DOF; small number equals smaller DOF.
3. Shutter Speed
Shutter speed refers to the amount of time the camera’s sensor is exposed to the scene you’re shooting. Shutter speed is measured in seconds (1, 2, 3, etc) and fractions of a second (1/10, 1/30, 1/60, etc). Bringing it back to elementary school math, remember that 1/10 is slower than 1/100!
Faster shutter speeds are great for capturing scenes in fast motion, such as a sprinter or a car race. Slower shutter speeds are used in low light situations (need to allow more light to hit the sensor), used to capture motion blur (such as the flow of water down a waterfall), and for other cool effects such as light painting. When shooting in lower shutter speeds (generally anything less than 1/60) it’s a good idea to use a tripod to prevent camera shake.
The trick to the exposure triangle is realizing that none of the three elements act independently – changing one normally means an adjustment of another. It might seem like a lot at first, but I promise it’s gets easier to control the more you practice. So grab your gear, take your camera off of auto mode, and go have some fun!