Depth of field (DoF)—the phenomenon responsible for achieving selective focus—can be a complicated subject to understand for beginners. It’s such a vast topic that people have even written books about it. Thankfully, there are simpler ways to explain it without requiring you to read pages and pages of boring information.
In this article, we’ll answer the most important questions you might have about DoF. We’ll also show you the quickest and easiest methods to achieve DoF when you’re taking photos, so read on and prepare to take some notes.
Depth of field is the distance between the closest and farthest objects in a photo.
Most definitions of depth of field are too technical for many to understand. But as a budding photographer, all you need to know is that it’s the zone in front of the camera that's sharp and any object that's not in that area is bound to be out of focus.
Also called focus range, depth of field can be adjusted mainly by using your lens. You can make it “shallow” to create a blurry background and foreground as shown in the photo below...
...or you can make it “deep” to keep everything in focus like this image:
Depth of field is generated in the lens and is determined by an opening called the aperture. Working like a mechanized iris, it controls the light coming into the camera and, in turn, affects the focus range: the wider (more shallow) the opening, the more out of focus the background is going to be.
The focal length (the distance between the lens and the sensor) of the lens also influences the DoF: a long lens typically produces a shallower field of focus than a shorter one. Therefore, a 135 mm. lens provides a softer background than its 50 mm. counterpart.
Another factor that affects the DoF is the camera-subject distance. You can always expect the amount of blur to increase the closer you get to the object you’re photographing. Inversely, the background becomes hazier the farther the subject is from it.
Apart from the lens and your distance from the subject, the sensor’s size also plays a significant role in the amount of DoF you’ll get. Typically, the bigger the sensor, the better background blur.
Digital cameras have different sensor formats: the most common ones are the smaller crop sensors often used by regular enthusiasts and full-frame sensors that most professionals prefer. Since a crop-sensor camera has a smaller area to record an image, it doesn't have the same amount of blurriness a full-frame camera can achieve even if they both use the exact lens.
Now that we’ve explained what DoF is and how it works, it’s time to use it. We’ll start with the most crucial component in achieving focus: the lens.
The lenses used for digital SLRs (or mirrorless cameras) typically have aperture rings that allow you to adjust the depth of field. On the ring, you’ll see different values called f-numbers. They often range from f/1.4 to f/22.
Selecting the lowest f-number such as f/1.4 (widest aperture) produces a shallow DoF and a blurry background, while using the highest value like f/22 (smallest aperture) creates a deeper DoF and a sharper background.
Once you’ve chosen your aperture, you can twist the focusing ring (found on the rim of the lens) to pick which part of the frame you want to be in focus. If you don’t adjust it, chances are, the entire photo is going to end up blurry regardless of your aperture size.
The hyperfocal distance—the range in front of the camera where the scene begins to be in focus—also plays an important role in achieving the level of sharpness that you want. Any particular lens’ hyperfocal distance depends on the aperture and the focal length of the lens.
For instance, if you have a 50mm. lens (focal length) set to f/22 (aperture) on a full-frame camera, the closest you can get to your subject while maintaining a sharp background is 12 feet—that is the hyperfocal distance, and you have to be that far away from your subject to keep the background sharp. If you get any closer than that, anything behind the object you're photographing may not be in focus.
Older lenses are perfect for quickly setting the hyperfocal distance since they have a range scale on the focusing ring. Simply align the aperture size to its corresponding distance on the scale according to your calculator, and you're ready to shoot. For example, if you're using a 50mm. with an aperture of f/22, just twist the focusing ring until it aligns with the 12 ft. mark on the scale.
If you're using a newer lens which doesn’t have a scale, point it at an object several feet away, like a tree in the background or a mountain in the foreground, then half-press your shutter button to let the camera adjust the focus automatically.
When everything in the scene is sharp, that means it has reached its hyperfocal distance. If your subject’s still blurry, you can either step back or point your lens farther away until it’s in focus.
Note that you can always download a DoF calculator to help you determine depth of field limits and distances at different aperture settings.
There are two ideal settings to use when adjusting DoF. The first and the easiest is Aperture Priority. In most cameras, it's often found on the mode dial (marked A or AV) next to the shutter. Once selected, it allows you to change the aperture while automatically choosing the right shutter speed for you.
The next setting you can select is manual mode, found on the same dial where aperture priority is. While you will have to change both the aperture and the shutter speed yourself, it’s the best setting to use if you want to bypass your camera’s auto exposure settings. For instance, if your aperture is at f/1.8 and the shutter speed at 1/50th but you want f/1.4 and 1/60th, then just switch to manual and personally set your preferred value.
A shallow depth of field is perfect for isolating subjects from the foreground and the background. It’s especially useful in portraiture or when the surroundings are visually distracting. The best aperture values for obtaining a good blur are f/1.4 to around f/5.6; the lower the number you choose, the fuzzier the background.
On the other hand, deep DoF is effective at keeping everything in focus. That’s why people prefer it when shooting landscapes or when they want the entire photo to look crisp. The aperture values often used for deep DoF are typically between f/8 to f/22. The higher you go, the more the background will be in focus.
Just remember that DoF differs from one lens to another. While some have a maximum aperture (the widest opening) of f/1.8 and a minimum (smallest opening) of f/22, others can go up from f/1.2 to f/32.
As we’ve discussed, focal lengths also affect the focus range of your optics. For instance, the background blur of a 50mm. lens set to the aperture of f/1.8 is much more prominent than that of a 35mm. with the same aperture value.
There are a lot of practical purposes for manipulating DoF, but there are just as many creative reasons to do it. A good number of photographers love blurring the background in their photos just because it looks pleasing to the eyes. It’s become such a popular aesthetic that they even have a name for it—bokeh.
Plenty of regular lenses are known for the quality of their bokeh. 35mm. and 50mm. are just a few of photographers’ favorites for creating creamy backgrounds.
However, there are also special lenses that produce interesting bokeh. One of them is called the catadioptric lens, which is known for creating distinct circular bokeh patterns such as the ones in this picture:
Then there’s the special 85mm. Petzval lens which produces curvilinear bokeh:
Apart from buying lenses known for their background blur, you can also create unusual bokeh patterns with a basic lens by making custom filters. Using a cardboard and scissors, just cut out a circle big enough to cover your front glass. Afterward, draw a shape you like in the middle and cut it out. Most people create smileys, hearts, and musical notes, but you can create your own as well.
Once you’re done with your filter, just place it in front of the lens. As soon as you blur the background, all the round-shaped lights will take the shape of the filter you designed.
Depth of field can be overwhelming even when explained in simplest terms. You’re not expected to learn every aspect of it in one go. For the meantime, this is all you really have to remember:
Keep in mind that the lower the f-number you select, the blurrier the background.
Don't let the technical terms intimidate you. As long as you take note of the simple equations above and use them frequently, you’ll have better grasp of depth of field in due time.