You already know that your choice in aperture affects the depth of field in your photos. Your aperture size can also be manipulated in order to use longer or shorter shutter speeds, depending on the situation you’re shooting in.
Let’s define some of the terms -
Aperture is the size of the opening at the very back of the lens which determines how much light strikes the camera sensor. The aperture can constrict (at high f-stop numbers) or dilate (at low f-stop numbers).
Shutter Speed is the speed at which your camera snaps a photo. When the shutter is open, all light entering the camera is allowed to strike the sensor. If too little light makes it to the sensor before the shutter closes the photo will be underexposed, and if too much light makes it to the sensor the photo will be overexposed.
By adjusting the aperture size, we can allow more or less light to hit the sensor in a certain time period, allowing us to manipulate shutter speed for either fast or slow shots. For example -
- When photographing sports, we can use a very large aperture to let lots of light in so that we can use a very fast shutter that will freeze motion without any motion blur.
- When photographing a stream, we can use a small aperture to allow for a longer exposure time (slower shutter) which will allow us to capture a smooth, blurred flow of the water in the stream.
- When photographing people at night, we can use a very large aperture in hopes of using a fast shutter speed which will freeze motion so that we can avoid motion blur from subjects. (Traditionally, exposure times are longer at night because the camera waits for more light to hit the sensor, but this will usually cause motion blur when people are moving in the photos.)