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Understanding and Utilising Deep Depth-of-Field

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One of the first questions people always ask when they get their new Digital SLR is “how do I get that blurry background?" A shallow depth-of-field has become the hallmark of “professional" photos. While the technique has it's advantages, by emphasizing it we're ignoring how to properly use depth-of-field.

What most people don't know is that when they upgrade from their point-and-shoot cameras, they are also accessing the ability to use a really deep depth-of-field. In this tutorial, we'll go deep into the uses of the deep depth-of-field and some corresponding techniques.

Achieving A Deep Depth-of-Field

Depth-of-field is controlled by your aperture. A very shallow depth-of-field requires a wide aperture like f/2.8 or wider. To achieve a very deep depth-of-field, you need an aperture setting of f/16 or smaller.

Keep in mind that the focal length of your lens also affects depth-of-field. Wide angle lenses usually have a deeper depth-of-field than telephoto lenses when they're set at the same f/stop. So it's easier to get a deep depth-of-field with a wide angle lens, and using a telephoto lens requires an even smaller aperture.

The DSLR Advantage

Achieving a shallow depth-of-field is used as big selling point for DSLRs, but most compact point-and-shoots also lack the necessary small f/stops to achieve a deep depth-of-field. Even the two “powerhouse" point-and-shoots, the Canon G12 and the Nikon P7000, only offer a minimum aperture of f/8.

The same goes for the $800 Leica D-Lux 5. But even Nikon's $100 18-55mm kit lens allows you to stop down to f/22. While there are some exceptions, the point-and-shoot market has largely neglected these feature on their cameras. The graph below shows some common minimum apertures on some common point-and-shoot cameras.

The Depth-of-Field Gauge

Another thing that's left off modern point-and-shoots and modern DSLR lenses is a depth-of-field gauge. This was a great tool on older lenses. As you can see below, there are lines on the lens for each f/stop. The bracketing lines get farther and father apart as the f/stop gets tighter.

On this lens at this focus setting, you can see that at f/22, anything further than 3 meters away will be in focus. This is incredibly useful for determining the limits of your depth-of-field and for zone focusing, which will be mentioned later.

Depth-of-Field Preview

There is an alternative to the depth-of-field gauge that remains on most DSLR, especially mid-range models and better. Most of these cameras have a depth-of-field preview function. Sometimes it's a dedicated button. In the case of my D700, you assign the function to your choice of several buttons. Check your owner's manual to find the function on your camera.

When looking into your camera to compose and focus, your camera's aperture is set wide open. When you press your shutter button, the aperture closes down just before shutter opens. When you press depth-of-field preview function, it closes down the aperture without tripping the shutter.

When set at smaller apertures, you'll see the image get darker, but also see what will be in focus in your final image.

Uses For A Deep Depth-of-Field

Using a shallow depth-of-field is like picking a word and shouting it, like “FACE" or “FLOWER". Using a deep depth-of-field is like using a word in a sentence, like “see the face of the worker in the factory" or “see the flower in the meadow after a rain."

Neither of these approaches is right or wrong. By using a deep depth-of-field, you must carefully craft your sentence. Make sure your sentence isn't too confusing or random. “The student looks at his test in a room with desks and other students and posters and bright fluorescent lights and he's holding a pencil." Not a great sentence.

Remember to keep it simple. There are no firm rules on when to use a deep or shallow depth-of-field. But I would encourage you to explore the deep depth-of-field option when you encounter some of the common situations below.

Backgrounds Matter

I often shoot concerts for a music promoter. Whenever he sees a shot of a musician with no background or context, he always says “that shot could have been taken in my basement." Using a deep depth-of-field can help make a background clear and add an additional layer of information and context to your photo.

The downside of this is that sometime backgrounds are busy or cluttered. In the following image, if I had been using a shallow depth-of-field while focusing on the worker, the story of the image would be ruined. The background tells you that the man was working on a train wreck.

Foregrounds Matter, Too

In keeping with the idea of maintaining simplicity in your images, you'll notice that most images only have two layers, a foreground and a background. You composition determines which one is most important.

Typically, the foreground element plays the main role, while the background is secondary. Flipping this around is good photographic technique, and many times using a deep depth-of-field is necessary to execute it well. In the image below, you can seen many layers, but the extremely close hand sets a theme that keeps you look further into the image for the more hands.

Telephoto Compression

All telephoto lenses “compress" a scene. Due to their nature, objects at different distances appear closer together when photographed with a telephoto lens. Using a deep depth-of-field allows to exaggerate this effect.

When there are two elements you want in the picture, but their distance is making it difficult, remember that using a telephoto lens and a deep depth-of-field can bring them closer together.

In the following image, the subject and the background were probably 5 meters apart, and the logo was probably half a meter wide. By backing up, using a telephoto lens, and a deep depth-of-field, I was able to make the logo and face appear closer together and nearly the same size.

Macro Focusing

Depth-of-field is drastically affected by distance. If you are 20 meters from a subject, f/4 may give you several meters that will be in focus depending on your lens. But when your focusing within one meter, f/4 may only give you 5-10 centimetres that will be in focus.

In other words, you get less depth-of-field the closer you're focusing. When doing very close, macro photography, using a deep depth-of-field is sometimes the only way to make a readable image.

The image below uses a great depth-of-field in order to showcase all the different elements in the frame. Had he used a shallow depth-of-field, the impact of all the different types of sushi would be lost.

Zone Focusing

Zone focusing is a technique that relies on using a deep depth-of-field. The technique is extremely easy to achieve with the previously mentioned depth-of-field gauge, but with a little practice you can also master it.

Strongly preferred by street photographers, zone focusing relies on a deep depth-of-field to make focusing much easier or even unnecessary. This allows you to shoot very quickly.

Basically, you stop down as much as you can in your given lighting situation. Then manually focus your camera to a medium distance. As long as your subject is within the depth-of-field range, it will be in focus.

The following image was taken from the hip. I set my aperture as tight as it would go on such a cloudy day, and then waited for the subject to enter the frame. I was assisted by the depth-of-field gauge on the old film camera I was shooting.

Pinhole: The Extreme

Pinhole cameras use a very tiny hole to make an image instead of a usual lens. A pinhole operates much like a very small aperture. Therefore, using a pinhole is the ultimate for achieving a deep depth-of-field. Pinhole allows everything to be in focus.

The downside to this is long exposures. But pinhole caps are available for DSLRs which in recent years have become great at higher ISO settings. And at those settings, acceptable shutter speeds can be achieved in bright sunlight.

Just keep in mind that pinholes come in different sizes, and those sizes correspond to the distance the pinhole is from the sensor or film. If you get the wrong size pinhole, everything at every distance will be equally blurry instead of equally sharp.

In this last image, the small plant was just centimetres away from the pinhole, and yet it is as in focus as the background. Details on both the leaves and the bricks of the building can be seen.

Getting In Deep

Depth-of-field is a principle of photography that will allow you to take your images to the next level. There's no one depth-of-field that's universally better than another. Using a shallow depth-of-field is great for certain situations, but using a deep depth-of-field also has a wide variety of applications.

I encourage you to practice using a really deep depth-of-field as much as you use a very shallow one. Figure out which way works best for a given situation.

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