The term depth of field refers to how much of the photograph is in focus. With a deep depth of field both the background and foreground are in focus. Like the example below.
With a shallow depth of field typically only the foreground is in focus while the background is blurry. See the example below.
Depth of field can be such a great and powerful tool for the photographer because it can focus the viewer’s attention onto a subject or a single spot within the picture.
How depth of field works
In many ways a camera works like a human eye. Both your eye and a camera have an iris that opens or closes to let more or less light in. This relates directly to how depth of field works. The depth of field is controlled by adjusting the aperture on your camera. When you change the aperture you are changing the size of the iris opening within the lens. The aperture setting is measured using a scale of f-stops. Smaller f-stop numbers mean a larger aperture (or that the iris is open more) while larger f-stop numbers mean a smaller aperture(or the iris is open less).
The larger the aperture the more shallow your depth of field will be. To Achieve a deep depth of field you will do the opposite and set a smaller aperture. Don’t forget when setting your f-stops smaller numbers mean a larger aperture (a shallow depth of field) while larger f-stop numbers means a smaller aperture (a deep depth of field). You can have a greater control over your aperture and f-stop numbers if you switch your camera to the aperture priority setting. This is usually dictated with an A (or sometimes an Av).
When to choose the right depth of field
Depth of field is one of the best tools a photographer can have. It’s important to know that different situations call for a different depth of field. When shooting portraits it’s great to choose a shallow DOF because it focuses on your subject’s face. Shallow DOF is also great anytime the background is very busy which could lead to a distraction from your subject. A busy city street or a party are examples of a busy background.
There are also times when you’ll prefer a deep depth of field instead. A landscape photograph for example. In landscape photography you want to capture the whole environment both close up and far away.
Depth of field can be a great tool within the photographers bag of tricks. You can focus on a single subject or capture everything in sight. But like many skills, achieving great depth of field takes practice and the proper equipment. Next time you’re taking pictures switch your camera over to aperture priority setting (A or Av) and experiment with depth of field.