The Beginner’s Guide to Understanding Depth of Field
I remember taking a group photo as a budding new photographer, then excitedly loading the images on to my computer only to discover that the people in the back rows were completely out of focus. I still remember that sinking feeling, and then the wondering, what did I do wrong?
The answer lies in depth of field. While either the autofocus or the manual focus determines what is in focus, it doesn’t determine _how much is in focus—_that’s where depth of field comes in. Those soft backgrounds in portraits? Or those crisp, almost completely-focused landscapes? Those are achieved through depth of field, but there’s actually more than one way to adjust the depth of field in any given image.
Curious? Here’s what you need to know to understand depth of field.
What is Depth of Field?
Depth of field is the range of distances that appears in focus. When you focus on an object, that object is sharply focused. But what about the object that’s, say an inch behind it? Or a foot behind it? Depending on your camera settings and lens type, the depth of field may be just millimeters, or a few dozen feet.
A shallow depth of field means that only a small portion of the image is sharply focused, while the background (and often foreground) are unfocused. Portraits commonly use a shallow depth of field, because that unfocused quality eliminates anything distracting from the background and draws more attention to the subject.
A narrow depth of field means that a large portion of the image is sharply focused, even for objects that are a little ways from the focal point. Landscapes use a narrow depth of field to show more of the scene, and group portraits should use a narrow depth of field to prevent the back row from being out of focus.
Factors That Affect Depth of Field
So, the depth of field determines how much of the image is in focus. But how do you adjust the depth of field? There’s actually more than one way to adjust the depth of field (plus another factor that’s set when you choose which camera to shoot with).
Aperture is the most well-known way to adjust depth of field, and also probably the easiest method. Remember aperture is the size of the opening in the lens—a larger opening lets in more light and vice versa. But aperture also plays a big role in the depth of field.
A wide aperture, or a low f-stop number, results in a shallow depth of field. Aperture settings like f1.8, and f2.8 let a lot of light into the image, but they also result in that unfocused background. At these wide apertures, an object needs to be very close to the original focus point in order to be sharp. That’s why, in portrait photography, it’s important to focus on the eyes—otherwise if the focus point is on the nose, the face may not be in focus with such a shallow depth of field.
A narrow aperture, or a high f-stop number, results in a narrow depth of field. (If you have a hard time remembering, just think narrow aperture = narrow depth of field.) Settings like f/8 and f/11 will leave much more of the image in focus. Objects don’t have to be very close to the original focal point in order to remain sharp—so that back row in the group photo is much clearer at f/11 than at f/2.8. Landscapes tend to use very high f-numbers so that the almost the entire scene remains sharp.
Aperture is just one depth of field element that the photographer has control over—distance plays a role too. Aperture controls the distance from the subject that objects will remain sharp, but simply adjusting the distance of these objects can change how focused or unfocused they are.
The distance between the subject and the background plays a role. For example, even at f2.8, if you take a portrait with the subject leaning against a brick wall, most of the details in the brick will still be noticeable, even at such a wide aperture. Ask the subject to stand a few feet away from the wall, however, and the wall becomes out of focus.
But the distance between the camera and the subject has an effect as well. If you’re not getting the out of focus background that you want and you can’t lower your aperture any more, you can just move closer to your subject. The closer you are to your subject, the shallower your depth of field will be.
There’s a lot of confusion surrounding the idea that the focal length of a lens also changes the depth of field. But the focal length of a lens doesn’t change the depth of field any more than getting close to your subject does. If you take an image at 300mm, then that same composition at 35mm by moving closer to your subject, the depth of field will be the same. If you take an image standing in the same location at 35mm and 300mm, the 300mm photo will have the shallower depth of field—but that’s from “getting closer” to the subject, not the actual focal length.
There’s one more factor to depth of field, but it’s not something the photographer can change between photos. The size of a camera’s sensor plays a role.
Cameras with larger sensors have a shallower depth of field than cameras with smaller sensors, taken at the same aperture and distance when applied to the same composition. It’s easier to get that unfocused background with a DSLR than with a point-and-shoot camera.
While you can’t change your camera’s sensor size like you can change the aperture, it’s important to understand, particularly if you switch between a point-and-shoot and a DSLR.
Depth of Field: Tips and Pitfalls
Understanding depth of field is essential to mastering photography. But there’s also a few tips (and a few pitfalls to put caution cones around) when it comes to depth of field.
Don’t make the depth of field too shallow when you need to focus quickly. When your focus point is off at f/1.8, it’s really off. But if your focus point isn’t quite right at f/8, you can still capture a sharp subject, thanks to the principals of depth of field. New photographers that need to focus quickly (i.e. for action photos) should use a narrower apperature (as the lighting allows) to ensure a sharp subject. As your confidence and focusing technique grows, then it’s okay to use wide apertures for action.
That unmarked button on your DSLR up close to the lens? That’s a depth of field preview button (on most modern cameras anyways). Under normal shooting scenarios, the camera doesn’t show you depth of field through the viewfinder. But pressing the depth of field button stops down the aperture, so you can see how sharp your background will be.
Don’t forget the foreground. Just as depth of field affects the background of an image, it affects the foreground too. If you’d like the foreground of your image to be sharp, use a narrow aperture. If you’d like the foreground to be out of focus, use a wide aperture. You can also adjust the distance between the subject and foreground, or the distance between the camera and the foreground, but that’s not always practical.
Double check to make sure that everything you want to be in focus, is in focus. If you’re shooting a portrait, the eyes and face should be in focus, and you may want to increase that f-stop number a bit to get the hair in focus too.
Depth of field is an essential element to understand, both to ensure the entire subject is sharp and to choose when the background is soft. A portrait may require a shallow depth of field, while landscapes are often best with a narrow depth of field. But there’s more than one way to adjust depth of field—aperture plays a role, but so does distance and sensor size. Experiment with depth of field to really grasp the concept—try shooting at different apertures, then try shooting at different distances. Before you know it, you’ll have another tool to add to your bag of photography tricks.
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