Aperture and Depth of Field are two terms that are often used together.
What is the aperture?
The aperture is the opening inside the lens that allows light to enter. Therefore, it is the aperture that lets you control how much light enters the lens – by adjusting the aperture size: a smaller opening (less light), a wider opening (more light). I’m sure you have seen “f” followed by a number. That number is called the f-stop. The F-number, f-stop, is how we measure the size of the aperture opening, which can be a little tricky. The number gets bigger as the opening gets smaller. f2, is a wider opening , and f11, is a smaller opening.
In order to get a visual understanding, look at the chart below:
To set Aperture Priority on your camera, turn the settings dial to Av. By choosing this setting, you control the depth of field with the aperture setting, and the camera will choose the best shutter speed (based on your aperture and ISO setting). This is the setting that I use most of the time.
Depth of Field
That leads us to aperture and how it affects the depth of field. A shallow depth of field uses a wider aperture, lower f-number. This means that that subject closer to the camera is in focus and the background is out of focus. A wider depth of field, larger f-number will bring more of the background into focus.