Introduction

Have you ever photographed a flower and wondered why only its center was sharp while the petals were blurry? Or, on the contrary, why everything in the scene appeared sharp when you wanted to isolate your subject?

In both cases, the answer lies in depth of field. In this article, you’ll learn what depth of field is, how it works, and how you can use it to improve your photographs.

What is depth of field?

One of the first things every photographer learns is that you need to focus your camera to get a sharp image. This focus point is directly related to depth of field.

Depth of field is the area of your image that appears acceptably sharp (the focus zone). Everything in front of or behind this zone gradually becomes blurred. That’s why focusing is essential: it determines where the sharp area of your image will be.

In reality, the scene isn’t simply divided into “sharp” and “blurry.” The area within the depth of field is sharp (the green zone in the illustration below), while objects become progressively more blurred as they move farther in front of or behind the focus plane (the red zones).

The blur in front of and behind the focus plane is known as bokeh, a Japanese word widely used in photography. When bright highlights are present in the background, this blur can create beautiful circular shapes known as bokeh circles.

The three factors that influence depth of field

Why does aperture change background blur?

The aperture of your lens is one of the most important factors affecting depth of field.

The wider the aperture, the shallower the depth of field becomes. Conversely, the smaller the aperture, the greater the depth of field. For example, landscape photographers often use smaller apertures to keep as much of the scene in focus as possible.

When you’re just starting out, it’s easy to mix up all these concepts. Personally, I prefer keeping things simple, so here’s the mnemonic that helped me remember:

• Small f-number = shallow depth of field
• Large f-number = deep depth of field

How does focal length affect depth of field?

Focal length also plays an important role. The longer the focal length, the shallower the depth of field becomes. Using a short focal length (also known as a wide-angle lens, 35 mm or less) gives you a larger area of sharpness. On the other hand, a longer focal length (a telephoto lens, 100 mm or more) produces a shallower depth of field.

Here’s the mnemonic that helped me remember:

• Telephoto lenses compress perspective, resulting in a shallower depth of field.
• Wide-angle lenses create a greater sense of depth in the image.

What happens when you move closer to your subject?

This is a very important concept, and it took me the longest to fully understand. With the same focal length and aperture, the distance between you and your subject also affects depth of field. The closer you get, the smaller the sharp area becomes.

Here’s the mnemonic that helped me remember:

• Close subject = shallow depth of field
• Distant subject = deep depth of field

Why does it become so extreme in macro photography?

As you may know, I’m passionate about photographing insects, frogs, and other tiny creatures. Macro photography is a demanding discipline, especially when it comes to depth of field.

Because the subjects are so small—sometimes only a few millimetres long—we usually use a relatively long focal length (I personally use a 105 mm macro lens) while working extremely close to the subject. This combination creates an incredibly shallow depth of field, often measuring just a few millimetres.

As a result, it’s not uncommon for only part of the subject to be in focus. Most of the time, photographers focus on the subject’s eye while the rest of the body gradually falls out of focus.

Fortunately, there are techniques to overcome this limitation. I explain one of them in detail in another article: focus stacking. It consists of taking a series of photographs while slightly shifting the focus point between each shot. These images are then combined to produce a final photograph with a much greater depth of field and an impressive level of detail.

How to use blur to guide the viewer’s eye

At this point, you might think that having a large depth of field is always the best option because it captures as much detail as possible. In fact, that’s exactly what I aim for when photographing landscapes.

But when I’m looking for a more artistic or painterly look, I do the exact opposite. I want the viewer to immediately understand what I want them to see, so I use foreground and background blur to naturally guide their eye toward the sharp area of the image: my subject.

By using a wide aperture, I can create soft foreground and background blur that adds atmosphere and helps draw attention to the subject.

FAQ

• What is depth of field?
  • It is the area of an image that appears sharp. Everything in front of or behind this area gradually becomes blurred.
• How can I control depth of field?
  • Small f-number = shallow depth of field / Large f-number = deep depth of field
  • Telephoto lens = shallow depth of field / Wide-angle lens = deep depth of field
  • Close subject = shallow depth of field / Distant subject = deep depth of field
• Why is depth of field so shallow in macro photography?
  • Because in macro photography, the subject is extremely close to the lens. Combined with a long focal length, this results in a very shallow depth of field, often only a few millimetres deep.