Depth of Field in Practice: From the Basics to Tilt-Shift

Depth of field is one of those terms that photographers use all the time—yet it represents much more than just a “blurred background.” Working with depth of field directly affects image clarity, the viewer’s attention, and the overall feel of a photograph. Let’s look at depth of field in a way that goes beyond tables and formulas.

In this article, we cover:

What depth of field is and why it’s about more than “blurred backgrounds.”
How to visualize the area of sharp focus in practice.
The difference between optical blur and motion blur.
How depth of field is affected by f-number (aperture), focal length, subject distance, and sensor size.
When to use shallow depth of field and when to use deeper focus.
What digital background blur can do.
How tilt-shift lenses change the plane of focus.

Depth of field is more than a technical parameter. It is one of the most powerful tools a photographer has to control the viewer’s attention—similar to how a director works with lighting on stage. Before we get into aperture, focal lengths, and sensors, let’s explain depth of field using a simple example.

What is depth of field—and how to see it in practice

Imagine a stick of butter representing the entire space in front of your camera. At first, everything appears equally out of focus—the camera hasn’t focused yet. When you focus, it’s as if you slice through the butter with a knife.

That slice represents the area that appears sharp in the photo. Everything within that slice—people, objects, details—is acceptably sharp. Anything in front of or behind it gradually blurs out of focus.

This is how depth of field works—not a single point, but a zone of space that appears sharp. Technically, we call it the plane of focus, but unlike a mathematical plane, it has measurable thickness.

*At f/2.8, that slice is very thin, resulting in a shallow depth of field.*

vThis sharp focus area can be as thick as a large slice of butter or extremely thin, almost razor-thin. The thickness of that “slice” is what we call depth of field.

*At f/4.0, the slice becomes thicker, resulting in a deeper depth of field.*

Everything outside this area falls into out-of-focus blur, commonly referred to as bokeh. This is what separates the subject from the background and creates that familiar sense of depth and space.

Depth of field vs. motion blur

It’s important to distinguish between optical blur caused by depth of field and motion blur. Optical blur is determined by f-number, focal length, subject distance, and sensor size. Motion blur, on the other hand, is caused by movement combined with a longer shutter speed. A classic example is panning, where you track a moving subject while using a longer shutter speed. The result can look similar at first glance, but the cause is completely different.

Don’t confuse motion blur with depth of field blur. In this panning shot, only part of the child is in focus because I used a long shutter speed and tracked the subject. Here, the f-number and focal length have no effect on the result.

The depth of field effect is best observed in detailed or close-up shots. The closer the subject, the more noticeable the difference between the sharp and blurred parts of the image are. It’s also clearly visible in photos taken with a telephoto lens, even though the foreground is often missing, helping to perceive the space in its entire depth.

A common misconception is that depth of field means “sharp in front, blurry in back.” In reality, the zone of sharp focus is sandwiched between two blurred areas—one in front and one behind. We tend to notice background blur more often because many compositions lack a visible foreground.

*300mm focal length, f/6.7. Both foreground and background can be heavily blurred. The depth of field is extremely shallow due to the telephoto lens.*

Depth of field is not a technical necessity, but a creative decision. Just like color or contrast, it influences what the viewer sees first, how long they stay with the image, and how they interpret the scene. Sharp areas naturally draw the eye, while the blurred parts recede into the background and create visual separation.

*A shallow depth of field helps separate the subject from the background.*

By working with depth of field, photographers can isolate their main subject from a busy background, simplifying the scene, and creating a more intimate feel. A larger depth of field provides context and spatial clarity. It’s not about which approach is better, but which better serves the photograph’s purpose.

Factors that affect depth of field: f-number, focal length, and distance

Depth of field does not occur by chance, but rather is the result of several interconnected factors. Aperture, or f-number, is one of the most important. Lower f-numbers, such as f/1.4 to f/2.8, produce a shallow depth of field suitable for portraits. As you increase the f-number, the depth of field expands, and more of the scene appears sharp. The lower the f-number, the thinner the zone of focus and the more gradual the transition into blur is. A higher f-number expands this area, bringing more of the scene into focus.

Focal length also plays a big role. Longer focal lengths make the depth of field appear shallower and emphasize background blur. That’s why portraits taken with a portrait or telephoto lens (45mm and higher) often look more three-dimensional than images taken with a wide focal length, even if the shot is similar.

Another important factor is subject distance. The closer you are to your subject, the shallower the depth of field will be. This is clearly visible in macro photography, where often only a very thin layer is in focus. Imagine taking two consecutive shots of the same subject with the same lens and f-number—but change your distance to the subject—the depth of field will differ.

Further reading: How To Get a Blurry Background with a Basic Lens

Sensor size and depth of field

Sensor size also plays a role. Larger sensors allow for shallower depth of field at the same framing and f-number. This is one reason full-frame images often look different from images taken with APS-C cameras or smartphones. However, this doesn’t mean larger sensors are always better. For wildlife or architecture photography, an APS-C sensor will suffice. For portrait or wedding photography, where subject separation is key, full-frame cameras are often required.

Digital blur vs. optical reality

Modern software and AI tools can simulate a shallow depth of field in post-production using masks or depth masks. Portrait mode on your smartphone works in a similar way. Editor’s Note: We described one of these methods for digital background blur in the article 3 Tips for Bringing Out the Main Subject in Your Photo.

Although the results are constantly improving, it is still a simulation. Artificial blurring often runs into problems with fine details like hair or glasses, in transition areas between sharp and blurred areas, or in understanding the unique structure of a scene. It cannot yet fully replace work with light, space, and optics.

Tilt-shift: Tilting the plane of focus

And now for something more specialized.

Tilt-shift lenses allow you to tilt the plane of focus relative to the sensor. Normally, the plane of focus is parallel to the camera sensor and perpendicular to the lens axis. But with tilt-shift, that plane can be angled in almost any direction.

In practice, this means you can keep an entire ceiling sharp, while the floor is blurred. You can also focus across a scene at head height, so you’re no longer slicing space straight across—you’re cutting it diagonally.

*The plane of focus is perpendicular to the camera.*

The effect can be visually striking, sometimes even surreal and confusing for the viewer. Tilt-shift lenses are not everyday tools, and they definitely don’t come cheap.

*The plane of focus is horizontal. The poles in the foreground, part of the frame, and the chimney in the background are all in focus.*

Tilt-shift lenses are a good reminder that there are rules for working with depth of field, but exceptions exist. And sometimes it’s precisely those exceptions that show us that depth of field is not a rigid rule, but a flexible tool you can deliberately control.

Further Reading: Make It Miniature With the Tilt-shift Effect

FAQ

What is depth of field? Depth of field is the range of space in front of the lens that appears acceptably sharp in a photograph. It is not a single point, but extends between the front and rear limits of acceptable sharpness.

How can I get a shallow depth of field? Use a low f-number (e.g., f/1.8–f/2.8), a longer focal length, move closer to your subject, and if possible, use a larger sensor.

What affects depth of field most? F-number, focal length, subject distance, and sensor size. These factors all work together.

Is bokeh the same as depth of field? No. Bokeh refers to the character of the out-of-focus areas. Depth of field describes how much of the scene is in focus.

What’s the difference between depth of field blur and motion blur? Depth of field blur is optical and related to focus settings. Motion blur is caused by movement of the camera or subject and long shutter speeds.

Can smartphones replicate shallow depth of field? Smartphones simulate a shallow depth of field using software. The results can look convincing, but fine details, glasses, and complex edges often reveal the difference.

What is a tilt-shift lens for? It allows you to tilt the plane of focus and control perspective—commonly used in architecture and for creative effects.