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One of the first things many photographers notice when they begin looking more carefully at photographs is that sharpness does not always extend evenly throughout an image.
Sometimes a person is perfectly sharp while the trees, buildings, or lights behind them seem to melt into a soft background. In another photograph, everything from the rocks in the foreground to mountains far in the distance may appear detailed and clear.
Both photographs can be correctly focused.
The difference is something called depth of field.
The phrase may sound technical when you first encounter it, but the idea behind it is actually fairly simple. Depth of field describes how much of the scene appears acceptably sharp in front of and behind the exact point where your camera is focused.
Learning to control depth of field gives you another way to guide the viewer through your photograph. Instead of simply deciding what to focus on, you begin deciding how much of the scene you want the viewer to notice clearly.
That makes depth of field both a technical tool and a creative one.
What Is Depth of Field?
Imagine that you are photographing someone standing outdoors several feet in front of a row of trees.
You focus carefully on the person's eyes.
If the person is sharp while the trees behind them become soft and blurry, you are seeing a shallow depth of field.
If the person is sharp and the trees behind them are also fairly clear, you are seeing a deeper depth of field.
A simple way to think about it is to imagine a zone of sharpness extending in front of and behind the place where you focused. Sometimes that zone is narrow. Sometimes it stretches much farther through the scene.
There is one important detail here. Only one exact distance is actually the camera's true plane of focus. Objects in front of and behind that point gradually become less sharp. Depth of field describes the range that still looks sharp enough to us when we view the photograph.
There is not an invisible line where the image suddenly changes from perfectly sharp to completely blurry. The transition happens gradually.
Fortunately, you do not need to calculate any of that mathematically to begin using depth of field effectively.
You mostly need to understand what makes that zone larger or smaller.
Shallow Depth of Field
A shallow depth of field means that only a relatively small portion of the image appears sharp.
Portrait photography is probably the most familiar example.
A photographer may focus on a person's eyes and use settings that allow the face to remain crisp while the background becomes soft and unobtrusive. The background is still there, but it no longer competes strongly with the subject.
This can help direct the viewer's attention exactly where the photographer wants it to go.
The same technique works with many other subjects. You might use shallow depth of field when photographing a flower, a pet, wildlife, food, a small object, or an architectural detail.
It can also be useful when the background is distracting.
Suppose you are photographing someone in a park, but there happens to be a fence, sign, parked car, or cluster of people behind them. If you can soften those background elements, they may become far less noticeable.
A shallow depth of field does not remove the background. It simply gives the background a quieter role.
Deep Depth of Field
A deep depth of field means that a larger portion of the scene appears sharp.
Landscape photography is one of the most common examples.
Imagine standing beside a lake with flowers in the foreground, trees farther away, and mountains rising in the distance. Instead of isolating one flower and allowing everything else to blur, you may want the viewer to appreciate the entire scene.
In that case, a deeper depth of field is usually more useful.
Travel photography, architecture, cityscapes, interior photography, and some group photographs can also benefit from having more of the scene appear sharp.
Neither shallow nor deep depth of field is automatically better.
They simply create different visual experiences.
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The same portrait can feel very different depending on aperture. At f/2.8, the background becomes soft and unobtrusive. At f/11, more of the surrounding environment remains visible and recognizable.
Aperture Is the Main Control
For most beginning photographers, the easiest way to start controlling depth of field is through the camera's aperture.
Inside your lens is an opening that controls how much light passes through the lens and reaches the camera sensor.
The size of that opening is described using numbers such as:
f/2.8, f/4, f/5.6, f/8, and f/11.
This is where photography vocabulary becomes slightly backward at first.
A small f-number means a larger lens opening.
A large f-number means a smaller lens opening.
So f/2.8 is a wider opening than f/11.
That feels upside down until you have used the settings often enough for them to become familiar.
For depth of field, there is an easier relationship to remember.
A lower f-number generally produces a shallower depth of field.
A higher f-number generally produces a deeper depth of field.
If you want to photograph a person and soften the background, you might try f/2.8 or f/4 if your lens allows it.
If you want much more of a landscape to appear sharp, you might begin experimenting around f/8 or f/11.
These are not rules carved into stone. They are starting points.
The aperture you choose will depend on your lens, available light, distance from your subject, focal length, and what you want the finished photograph to look like.
Controlling Depth of Field on
a Nikon Camera
On many Nikon cameras, one of the easiest ways to experiment with depth of field is to use Aperture Priority mode, which is usually marked with the letter A.
In this mode, you choose the aperture and the camera automatically selects an appropriate shutter speed to produce the exposure.
That makes Aperture Priority especially useful when you are learning.
You can concentrate on changing the f-number and watching what happens to the background without having to manually adjust every exposure setting.
Once the camera is set to A mode, use the appropriate command dial to change the aperture. The exact dial or control varies somewhat between Nikon models, so your camera manual is the best guide for the physical controls on your particular camera.
Try focusing on the same subject and making several photographs at different apertures.
Start with a low f-number such as f/2.8 or f/4.
Then try f/5.6.
Move to f/8.
Finish at f/11.
When you compare the photographs later on a larger screen, pay attention to the background rather than just the subject.
You should begin to see the zone of apparent sharpness expanding as the aperture becomes smaller.
Controlling Depth of Field on
a Canon Camera
Canon cameras work on the same photographic principle.
On many Canon models, Aperture Priority is labeled Av, which stands for Aperture Value.
Once you select Av mode, you choose the aperture while the camera selects the shutter speed.
If you want a softer background, try moving toward a lower f-number.
If you want more of the scene to remain sharp, move toward a higher f-number.
Again, the exact button and dial arrangement will vary depending on the Canon model you are using.
The important idea is not the location of the control.
Whether your camera says A or Av, you are telling the camera essentially the same thing:
You want control over aperture because aperture is important to the way the photograph looks.
The camera can help handle the corresponding shutter speed.
Aperture Is Not the Only Thing
That Affects Depth of Field
Aperture receives most of the attention when photographers discuss depth of field, but it is not working alone.
Your distance from the subject also makes a major difference.
Move closer to your subject and depth of field generally becomes shallower.
Move farther away and depth of field generally becomes deeper.
This is very easy to demonstrate with something as simple as a flower.
Photograph the flower from several feet away, then move much closer and focus again.
Even if you leave your aperture unchanged, you may notice that the background appears softer as you move closer.
This is one reason close-up photographs often have very shallow areas of sharpness.
Your lens and focal length also influence the appearance of depth and background separation.
Longer focal lengths are often used when photographers want strong subject isolation. Wider-angle lenses are commonly used when photographers want to show more of the surrounding environment.
The exact relationship between focal length and depth of field becomes more complicated when you start considering subject distance, camera position, and how large the subject appears in the frame.
For a beginner, the practical lesson is enough:
Aperture, your distance from the subject, and your choice of lens all work together.
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Depth of field affects more than portraits. At f/2.8, the foreground flower stands apart from a strongly blurred background. At f/11, the garden, bench, path, lake, and distant landscape appear much more defined.
Depth of Field and Bokeh Are Not
Exactly the Same Thing
You will often hear the word bokeh when photographers talk about shallow depth of field.
The two ideas are related, but they do not mean exactly the same thing.
Depth of field describes how much of the photograph appears acceptably sharp.
Bokeh describes the visual character or quality of the areas that are out of focus.
Those soft circles of light you sometimes see behind a portrait are part of the bokeh.
Different lenses can render those out-of-focus areas differently.
For Photography 101, the easiest thing to remember is that a shallow depth of field can help create a blurred background, while bokeh describes what that blur actually looks like.
Remember That Aperture
Also Changes Exposure
There is another reason aperture matters.
Changing the aperture changes how much light enters the camera.
A wide aperture such as f/2.8 allows more light through the lens.
A smaller aperture such as f/11 allows less light through.
If you are using Aperture Priority mode, the camera will usually respond by changing the shutter speed.
For example, if you move from f/4 to f/11, the camera may need to use a slower shutter speed because less light is passing through the lens.
That can become important if you are holding the camera by hand or photographing something that moves.
A shutter speed that becomes too slow may introduce camera shake or motion blur.
You may need to increase ISO, stabilize the camera, use a tripod, or choose a somewhat wider aperture.
This is one of the reasons photography settings are so interconnected.
Aperture affects depth of field, but it also affects exposure.
Shutter speed affects exposure, but it also affects motion.
ISO affects exposure, but increasing it can influence image quality.
Photography becomes easier when you stop thinking of those settings as isolated controls and begin seeing how they work together.
Why Not Just Use f/22
for Everything?
Once someone learns that higher f-numbers create greater depth of field, a natural question follows.
If f/11 gives me more sharpness through the scene, why not simply use f/22 whenever I want everything sharp?
Because photography always seems to hide another wrinkle behind the next curtain.
Very small apertures can introduce an optical effect called diffraction.
Diffraction can reduce fine detail and overall image sharpness, even though the photograph technically has greater depth of field.
That is one reason landscape photographers do not automatically choose the smallest possible aperture.
For many situations, something around f/8 or f/11 is a useful place to begin experimenting.
The best aperture depends on the scene, lens, camera, and how much depth of field you actually need.
A Simple Practice Exercise
You can learn more about depth of field in fifteen minutes of practice than you can by memorizing a page of technical definitions.
Find something around your home or outside that has visible background detail behind it.
A coffee mug on a table works.
A flower works.
A person standing several feet in front of trees works even better.
Put a Nikon camera in A mode or a Canon camera in Av mode.
Focus on the same point for every photograph.
Take your first photograph using the lowest f-number your lens allows.
Then take additional photographs at f/4, f/5.6, f/8, and f/11, if those apertures are available.
Try not to change your position or composition between photographs.
Afterward, view the images on a larger screen.
Look carefully at what happens behind the subject.
You will probably find that depth of field makes much more sense once you can see the differences side by side.
Depth of Field Is Ultimately
a Creative Decision
The goal of photography is not to make every part of every photograph perfectly sharp.
Sometimes you want the viewer to see everything.
Sometimes you want the viewer to see one thing.
A sweeping landscape may invite the eye to wander from the foreground all the way toward the horizon.
A portrait may become much stronger when the background fades quietly away and leaves only the person's expression demanding attention.
A flower may stand out beautifully when everything behind it becomes a wash of color.
Depth of field helps you make those decisions intentionally.
As you become more comfortable changing aperture, moving closer or farther from your subject, and experimenting with different lenses, depth of field begins to feel less like a camera setting and more like part of your visual language.
That is an important step in learning photography.
You are no longer simply asking whether the photograph is in focus.
You are deciding where you want the viewer to look and how you want the viewer to experience the scene.
And that is when one more camera setting begins turning into one more creative tool.
