What is depth of field in photography?

You’ve probably seen a lot of photos with soft, blurred backgrounds. With the right setting, they can look pretty dreamy with colorful circles (called bokeh) behind the subject. Perhaps most importantly, they can draw your attention instantly to the subject in the picture and help hide distracting things in the background. This image style uses one end of the photographic depth of field (DOF) spectrum, ranging from shallow to deep.

Apple’s portrait mode brought this look into the mainstream by allowing shallow depth of field for smartphone users, and not just those with expensive cameras and lenses. Unfortunately, the way Apple and other smartphones achieve this look isn’t a very accurate representation of what depth of field is or how you actually achieve it.

Related: Outsmart your iPhone camera’s overzealous AI

What is depth of field in photography?

Shallow depth of field

Three people stand in a row, the middle person is in focus.
This is an example of a shallow depth of field image where neither the closest (foreground) nor the farthest (background) subject are in focus. This image was taken at f/2.8. Had the photographer used an aperture like f/16, all three subjects would likely appear in focus, or nearly so. Kelvin Murray/Getty

Depth of field can get very complicated (there’s even a math formula), but it doesn’t have to be. It is defined as the distances between the closest and farthest subject that will be acceptably sharp in focus. In even simpler terms, it’s the amount (or depth) of a scene that is in focus.

As previously mentioned, the depth of field can range from shallow to deep. A shallow depth of field means that only a small – or narrow – area of ​​the scene is in focus. This is the kind of image you see in portrait modes, where the subject is in focus but the background is blurred. On smartphones, this look is created using AI and artificial background blur. However, there are ways to control depth of field in a more technical way via the three factors that affect it: focal length, aperture, and distance.

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Deep depth of field

On the other hand, a deep depth of field generally means that most of the scene is in focus. Landscape photographers often use a deep depth of field to show sweeping, dramatic views. You will also see the deep depth of field in many photojournalism images.

View of Mont Blanc with fresh snow
A deep depth of field is often used in landscape photography. For example, this image was taken at f/19. Notice how almost everything is in focus? Aaron Foster/Getty

It’s important to remember that depth of field is actually a spectrum. You can focus on just the tip of a person’s nose, the entire person, the entire scene, or anything in between. We tend to only refer to the extremes when we talk about depth of field in photography, but there is also a middle ground.

What is not depth of field?

When I was teaching introductory photography courses at a university, the concept of depth of field was a bit confusing for students. Very often they would focus on the background of an image and if it was in focus they would assume the photo had a large depth of field. It’s common to think that focusing deep in the background of the picture means a large depth of field. But it’s wrong.

Decouple focus distance from depth of field

This is where Apple – and to some extent other smartphones – have created some confusion. By default, when you point your iPhone at something, it focuses on the object closest to the phone. So without overriding the default setting, the foreground will always be sharp and the background blurry. This seems to have led to the assumption that all shallow depth of field images have a blurred background. That’s not the case.

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Portrait of a woman with blurred background
This shallow depth of field portrait was shot at f/1.4. If the photographer had instead focused on the windows in the background and left the subject blurry – an odd compositional choice but irrelevant to us – this photo would still have a shallow depth of field. Luis Alvarez/Getty

Because of this confusion, I also think it’s helpful to point out what depth of field isn’t. In photography, the depth of field is not Where you concentrate Instead it is how much is in focus. You can have shallow depth of field when something directly in front of the camera is in focus and the background is blurry, but you can also have the opposite, a sharp background and a blurred foreground. And of course, anything in between can also have a shallow depth of field.

What is the easiest way to control the depth of field?

Close up of red flowering plant in field, Los Angeles, California, United States, USA
This f/2.8 image has a fairly shallow depth of field. However, the two flowers on the far right are both in focus despite being at different distances from the camera. Had the photographer wanted to fully isolate the orange flower in the center, he could have used a larger aperture like f/1.4. Catherine Lacey Dodd/500px/Getty

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The focal length of your lens and the distance from the camera to the subject are both factors that affect depth of field. In general, the longer the lens, the more “separated” a subject will appear from its background or foreground. In terms of distance, the farther the subject is from the camera and/or background, the more isolated they appear.

However, the easiest way to adjust DOF on the fly is to “open” or “stop down” the aperture. Opening the aperture means using smaller F-numbers like f/2, resulting in a larger diameter opening in the lens. The more light that enters the lens, the shallower the depth of field.

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Stopping down the lens requires using larger F-numbers such as f/11 for a smaller diameter aperture. This results in a deeper depth of field. For example, an aperture of f/1.4 lets in more light while focusing less of the frame. While an aperture of f/16 lets in less light, most of the scene will likely be sharp.

Why is depth of field important?

Since your phone can figure things out all on its own (or so it thinks), why does it even matter? Knowing what depth of field is and how to manipulate it can be an easy way to dramatically improve your images. With the right depth of field—along with clever framing—a photo can go from boring and linear to creative and interesting. On your phone, you can tap where you want to focus to override the default setting, resulting in a more unique photo. It’s a simple trick that can make a big difference.

Understanding depth of field becomes even more important when using a dedicated camera instead of your phone. Cameras don’t have built-in AI to artificially blur the background like your phone does. So if you want this look, you have to do it the old fashioned way. Glad you’re a genius at it now.

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