A Beginner’s Guide to Depth of Field
- Marianne Stenger
- 16th September 2019
What is Depth of Field?
At its simplest, depth of field (DoF) is the zone of acceptable sharpness in a photo, or in other words, how much of your image appears in focus. Although your camera can only focus on one thing at a time, there will always be an area in front of and behind your point of focus that also appears acceptably sharp, and it’s this that is referred to as depth of field.
Shallow vs. Wide Depth of Field
When setting up a shot, photographers always have the option of either bringing everything into sharp focus, or limiting sharp focus to just one area.
For example, with portraits or macro photographs, you’ll often notice that only one specific area of the image is in focus, and this is known as a shallow or narrow depth of field. In other types of images, such as group shots or landscape photographs, you’ll usually see sharpness throughout the whole image, and this is known as a deep or wide depth of field.
There are three main things that affect the depth of field in an image; aperture, lens focal length, and the distance between the camera and the subject. Understanding how and why these variables affect depth of field will give you greater creative control over your images:
The easiest way to control the depth of field is to adjust the aperture. When you use a wider aperture, which is indicated by lower f-stop number such as f/2.8 or f/1.8, your plane of focus will be narrower and most objects in front of and behind your subject will fade out of focus.
When you use a narrower aperture, which is indicated by a higher f-stop number such as f/20 or f/22, your plane of focus will be wider and virtually everything in front of and behind your subject will appear acceptably sharp.
The focal length of a lens refers to the distance in millimetres between the lens and the image sensor when the subject is in focus. A 24mm lens has a relatively short focal length and can capture more of the scene in front of you. A 300mm lens, on the other hand, has a much longer focal length and magnifies your subject, thereby capturing less of the scene in front of you. Because longer focal lengths magnify focus differences, they tend to result in a shallower depth of field.
The distance between the camera and the subject is another thing to keep in mind, because the closer your subject is to your camera, the shallower the depth of field in your image will be. A good exercise to help you visualise how this works is to hold up an object at eye level and arm’s length and slowly move it closer. Do you notice any change in the depth of field as the object moves closer?
Experimenting with Depth of Field
The best way to familiarise yourself with the concept of depth of field and learn how to control it is to start experimenting with different camera settings, lenses and distances to see how these variables affect your images.
If you’re not sure where to begin, start by choosing one object to focus on. This could be a person, animal, or inanimate object such as a tree or bench. Now take a photo of your chosen subject at both the minimum and maximum aperture that your lens allows.
Observe how the depth of field changes at different apertures and think about the scenarios in which you would use each one. If you have more than one lens, you can try this same exercise using different lenses and moving closer to or further away from your subject.