What is depth of field in photography?

After discussing exposure in photography in detail, along with the three settings that define it — shutter speed, aperture and ISO sensitivity — let’s dive a little deeper. To continue with the basics, today we are going to talk about depth of field. If you have never heard this term before, you still use it every time you take a photo. Remember when your camera focuses as you press the shutter button halfway down? That is part of it. Depth of field also helps you control how much of your image appears sharp.

This article explains everything you need to know about depth of field: what it is, why it matters, how to adjust it on your camera and which settings influence it.

After that, you should feel much more comfortable using depth of field creatively. Well… missed focus can still happen. It still happens to me too!

If you are new to photography, you may already know that using a wide aperture — a small “f/” number — lets you play with depth of field. However, aperture is not the only factor to take into account. In this article, I explain:

• what depth of field is in photography and why it is useful to control it,
• how to adjust it on your camera,
• which settings influence it.

Let’s get to the heart of the matter in a simple, not-too-technical way. So, what is depth of field? Put simply, it is the area of the image that appears acceptably sharp. In reality, some parts of your scene will be in focus, while others will gradually fall out of focus. You could also describe it as the distance between the nearest and farthest elements that still look sharp. Clear enough? On paper, it is not much more complicated than that.

You may wonder why mastering this concept matters in photography, and when you should use it. Let’s start with why. If you understood the definition above, you can already see that controlling depth of field mainly allows you to isolate and highlight a subject in a photo. How? By making that subject stand out as sharp — or, in some cases, deliberately blurred — within the image. If the subject you want to highlight is sharp, while other areas of the frame are blurred, it will naturally draw more attention.

Two examples of genres where depth of field is often shallow: macro photography on the left and food photography on the right.

As for the genres where depth of field is especially useful, I would mention the following:

• Macro photography: a very specific field where the idea is often to highlight a tiny detail,
• Portraits: the focus is generally placed on a detail of the person, often the eyes, while the rest is slightly blurred,
• Food photography: this type of image often focuses on a precise detail or part of a dish,
• any scene where the background or foreground is not very aesthetic and you want to blur it,
• and, more generally, any situation where you want to highlight a detail, whether it is part of a landscape, a specific urban scene or another subject.

As mentioned in the introduction, the aperture you choose when shooting has a major influence on depth of field. It is also one of the easiest settings to control once you start taking photos.

So, how do you change the aperture on a DSLR or mirrorless camera? Mainly by switching to “A” mode on Nikon, or “Av” mode on Canon, to name the most common labels. There is nothing too complicated here: turn your camera’s mode dial to the right mode, then adjust the aperture:

• The smaller the “f/” number, meaning the wider the aperture, the shallower your depth of field will be -> you get more blur.
• Conversely, if you want a large depth of field, for example in landscape photography, choose a smaller aperture such as f/11 or f/14 -> more of the scene will be sharp.

A simple way to remember it is this: the smaller the number after “f/” (for example f/2.8), the shallower the depth of field. And vice versa. For the same photo, taken from the same position with the same sensor size, depth of field will be shallower at f/4 than at f/11.

This is the main setting you can easily control. However, it is not the only one that influences depth of field in an image.

We have just seen that aperture is one of the main settings for blurring a background and highlighting a subject in a photo. Now let’s look at the four other factors that can influence depth of field.

This is one of the factors that most strongly influences depth of field and the look of the background blur, or bokeh. Try photographing the same subject from 30cm away and then from 2m away, while keeping the same settings, the same background distance, the same camera body and, of course, the same focal length. The difference is obvious at first glance. Just look at the two pictures below.

As you can see, the closer you are to your subject, the shallower the depth of field becomes. Conversely, the farther you move away from your subject, the greater the depth of field becomes. Yes, I have a three-year-old child, so I used one of his toys 😎. You can clearly see that my son’s car is entirely sharp in the photo taken from farther away, while only part of the same car is in focus in the photo taken from 30cm.

A splendid masterpiece in my living room: on the left I am 30cm from the subject; on the right I am 1.5m away.

You might be wondering what happens if you use a zoom. You can try the same test again: photograph a subject from 1m away, then step back to 3m and zoom in to get roughly the same framing as in the first image. You will eventually notice that the results are almost identical.

In other words, if you move farther back but use a longer focal length by zooming in, the results in terms of depth of field are very similar. By zooming in, you also reduce the depth of field. I explain this point in more detail below.

This is another important point to understand in photography. Remember this: when you take a photo, you focus on the area you want to appear sharp. So far, so good. But if you look more closely, especially when using a wide aperture, you will see that the blurred background is not uniformly blurred. Let me explain: if you look carefully, you will notice a gradual transition into blur.

The elements just behind your focus point will be only slightly blurred. Then, the farther they are from the focus area, the blurrier they become. This is especially noticeable in close-up portraits shot wide open — in other words, with a small f-number to blur the background as much as possible.

In the picture above, you can see that the focus was placed on the eyes. As soon as you move away from that focus area, the rest of the face begins to soften slightly, such as the cheeks or the nose. Move a little farther back, towards the temple for example, and the blur becomes even more visible. Finally, look at the hair or the ears: they are even blurrier.

Another example is this crate of cherries — which, by the way, I dream about — photographed at a market. You can clearly see the focus area in the center of the image. As you move away from this sharp area, the cherries become blurrier and blurrier, almost disappearing into soft circles at the back of the frame. Notice, too, that blur does not exist only in the background. You can also see in the photo that the foreground, just before the sharp cherries, becomes increasingly blurred as it moves away from the focus area.

So, the conclusion is simple: the farther your background is from your main subject, or more precisely from the focus area, the more blurred that background will appear. The same applies to portraits, landscapes or market scenes. If you understand this, you should be able to use it in your next photo shoot. To help you: if you want to isolate a subject and highlight it with a wide aperture, try to choose a composition where the background is as far away as possible from the area you are going to focus on.

The third point that influences depth of field is the focal length you use. This is closely linked to the two points above. You will notice that long focal lengths, such as 100mm, 200mm, 300mm or 600mm telephoto lenses, can create a very shallow depth of field even with relatively small apertures, such as f/8.

Keep this in mind: the longer the focal length, the shallower the depth of field. The shorter the focal length, the greater the depth of field.

Here is another very serious test, this time with one of my son’s stuffed animals. I am using a 250mm focal length at f/8, which is a relatively small aperture. Even so, I still manage to create a nice blur in the background. Try shooting at f/8 with a 15mm lens and you will never get this kind of blur. The longer the focal length, the more depth of field is reduced.

Be careful though: I am talking about shooting from the same position. Let’s take a concrete example to illustrate this with a quick calculation. You place yourself at a fixed spot and photograph your child 10m away with a 100mm lens at f/2.8, for example. You get a depth of field of 1.69m. In simple terms, your photo will be sharp over a distance of 1.69m, a little in front of and a little behind the focus point, as shown by the values “Depth of field in front” and “Depth of field behind”. So far, so good. Now you decide to use a shorter focal length, say 50mm, to photograph your child from the same position. Your depth of field increases to 7.62m, far beyond the 1.69m you had with the 100mm. This shows that, from the same position, the longer the focal length, the shallower the depth of field will be, and vice versa.

However, you also have to remember that if you shoot from the same position, your field of view with a 100mm lens will be much narrower than with a 50mm lens. With the 50mm, your child will appear much smaller in the frame. Of course, if the subject occupies the same proportion of the image, depth of field will be very similar with a 50mm or a 100mm. But to get the same framing with a 50mm as with a 100mm, you will have to move much closer to your child. You see what I mean? In the conclusion, I share an excellent depth of field simulator that you can use to test these differences, especially depending on the focal length used. I often use this one (the two images below come from it).

That said — and I really should illustrate this with a comparison photo — you can get a very similar depth of field with a 50mm and a 100mm if the framing is the same, but only by moving. In this case, with a 50mm, if you move to about 5m from the subject, you get the same depth of field as with your 100mm at 10m. However, when comparing the two backgrounds, you will still notice that the one shot with the 100mm looks softer and blurrier. This is simply because the longer focal length magnifies the background blur.

The last point that is sometimes forgotten, but which also has a major impact on depth of field, is sensor size. Of course, you always need to compare like with like, and many people forget to take sensor size into account, especially when comparing a full-frame body (24 x 36mm), an APS-C body (15.7 x 23.7mm) and a Micro Four Thirds body (MFT, 13 x 17.3mm). These dimensions are very different: there is roughly a factor of two between a full-frame sensor and an MFT sensor, as found in many Panasonic and Olympus mirrorless cameras, among others.

I’m not going to dive into complex calculations to demonstrate this, but I’ll try to explain the idea as simply as possible with two screenshots from a calculator. Sensor size influences your field of view. For example, if you shoot from the same position and want the same framing of your child with a full-frame body and an MFT body, you will need to use a focal length twice as short on the MFT body because the sensor is half the size. For example, you would use a 100mm lens on full frame and a 50mm lens on MFT. Using a shorter focal length simply increases your depth of field, as shown in the previous section.

You may be thinking: that’s all very nice, but so what? The idea is simply to show that you cannot compare depth of field, and therefore background blur, between different sensor sizes without taking sensor size into account. If I go back to my earlier example and keep the same distance from the subject:

• on a full-frame body, with a 100mm lens at f/2.8, you get a depth of field of 1.69m,
• if you use an MFT body with a 100mm lens at f/2.8, you get a depth of field of 0.84m, so it is shallower,
• however, the framing is not the same at all, and the photo taken with the MFT body will appear much more zoomed in,
• to get the same framing with your MFT body as with your full-frame body, you need to use a 50mm focal length, which is twice as short,
• in that case, however, you get a depth of field of 3.48m, which is more than twice as much as with the full-frame body,
• so, for the same framing and the same aperture, you will get an image that is sharper overall, with less background blur, on an MFT body than on a full-frame body.

I’ll stop here so as not to make things too complicated, but there would actually be more to say, such as how to find the equivalent depth of field between a full-frame body and an MFT body when shooting the same subject from the same position, for example a singer at a concert.

If you had to remember only one thing, it would be this: for the same framing and settings, the larger the sensor, the shallower the depth of field. This is why, in difficult lighting conditions such as concerts or indoor portraits, shooting with a full-frame body and bright lenses can be an advantage. For example, imagine you are trying to photograph a portrait of someone at a concert and you are using an 85mm f/2 lens on a full-frame body to reduce depth of field and create a nice background blur. To get the same result with an MFT body and the same framing, you would need to use a focal length of about 42.5mm, which is twice as short, but also an aperture around f/1 to get the same depth of field. In practice, this kind of lens is rare and often expensive, even though there is a 42.5mm f/1.2 lens that costs more than 1000€… while the 85mm f/1.8 is almost three times cheaper. Want to know more? I wrote an article about camera sensor size in the “Photography equipment” section of the blog.

To better understand and refine your grasp of this concept, I invite you to spend some time on this depth of field simulator.

I am coming to the end of this article on depth of field, a complex but essential concept when learning photography. I hope the definitions and examples are clear enough. If you would like more information or clarification on the subject, feel free to leave a comment at the end of the article. Here is a simple table summarizing the article.

If you have not yet mastered all the exposure settings, a quick reminder about aperture in photography is essential, isn’t it?

See you soon, and happy shooting.

Written by Sylvain PONS

I've been passionate about photography since 2010, learning as I went along. Today, I dedicate myself to guiding others in their choice of camera gear and sharing a variety of tips to improve their photography skills.

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