Depth of Field: What It Is and How to Control It
Depth of Field: A Photographer’s Powerful Tool
Depth of field (DOF) is one of the most effective tools a photographer can use to control the look and feel of an image. It can guide a viewer’s eyes, set the mood, and even change how a scene is perceived. Yet, while many photographers know what depth of field is, not everyone fully understands how to harness its power.
Landscape photographers are often more familiar with depth of field since it plays a huge role in wide, detailed shots. However, mastering depth of field is crucial in nearly all photography genres, from macro to portraiture.
In this guide, we’ll explore:
- What depth of field is
- Why focal length matters
- The concept of hyperfocal distance
- The 1/3 Rule and how to use it
- Why the ‘Infinity’ setting is critical to depth of field
- How to place the depth of field window in your frame
- Aperture selection and the risk of overusing shallow depth of field
- How to use apps to create depth of field effects (and what to avoid)
What Is Depth of Field?
Depth of field (DOF) refers to the range of distance in a photo that appears sharp and in focus. This “window” of focus stretches between the closest and farthest objects that are clear in your image.
The size of this depth of field window can vary depending on several factors:
- Lens focal length
- Distance between the camera and the subject
- Background/foreground distance from the subject
- Aperture setting
- Camera sensor size
While it’s possible to calculate depth of field using a formula or apps, in most cases, you can achieve great results with a basic understanding and a few practical tips.
The key to mastering depth of field lies in understanding how changes to any of the above five factors affect the size of your depth of field window.
Focal Length and Depth of Field
Key Lesson: The shorter the lens’s focal length, the larger the depth of field at a given aperture.
For example, imagine focusing on a subject 15 feet away:
- A 20mm lens at f/8 will have a larger depth of field than a 50mm lens.
- A 50mm lens at f/8 will have a larger depth of field than a 135mm lens.
So, the shorter the focal length, the larger the depth of field window. Conversely, a longer lens will result in a shallower depth of field, which is useful for isolating subjects in portrait photography.
Practical Example: Portrait of Your Dog
Suppose you’re shooting a portrait of your dog, who’s 15 feet in front of you. You want to use your 200mm lens to blur out the background, but you don’t have enough depth of field to keep both eyes in sharp focus at f/8. How can you fix this?
You have several options:
- Use a smaller aperture (larger f-stop) like f/16 to increase the depth of field.
- Move further away from your subject, which increases the depth of field but might bring unwanted background elements into view.
- If you're using an APS-C sensor, your depth of field will be larger compared to a full-frame sensor at the same aperture.
Choosing to stop down to f/16 is likely the best choice here.
What Is Hyperfocal Distance?
While not everyone needs to calculate hyperfocal distance regularly, it's helpful to know what it means.
In simple terms, hyperfocal distance is the closest focus point where everything from that point to infinity will appear sharp. Landscape photographers often use it to ensure maximum sharpness throughout the image.
For most everyday photography, though, calculating hyperfocal distance is unnecessary. Relying on rules like the 1/3 Rule or using the depth of field preview button on your camera is more practical.
The 1/3 Rule: A Simple Trick for Depth of Field Placement
The 1/3 Rule is an easy way to gauge how your depth of field will fall. The idea is simple:
- About 1/3 of the depth of field falls in front of your focus point.
- The remaining 2/3 falls behind your focus point.
Key Lesson:
Using the 1/3 Rule is a quick way to ensure the right parts of your image are sharp, especially in portraits or landscapes. In portraiture, for example, you can place the critical focus on the subject's eyes and ensure that everything from the tip of the nose to the ears falls within the depth of field.
The Infinity Setting and Depth of Field
The Infinity setting on your lens is critical when working with deep depth of field, particularly in landscape photography. The infinity mark tells you where to set the focus so that everything from a certain point to the farthest areas of the image is sharp.
Example:
Suppose you're photographing a model in front of a basketball hoop using a 35mm lens at f/4. By setting your focus just before infinity on the focus ring, you can ensure that both the model and the hoop remain in sharp focus within the depth of field window.
Overusing Shallow Depth of Field
Shallow depth of field, especially with wide apertures like f/1.8 or f/1.4, is popular in portrait photography. However, it’s easy to overdo it. Take the example of a portrait where the background is artistically blurred, but the subject becomes a mere blur themselves due to an aperture as wide as f/1.6.
Key Lesson:
For the best image quality, most lenses perform optimally between f/5.6 and f/11. While shallow depth of field can create stunning portraits, don’t overuse it. Using mid-range apertures often results in sharper images and a more balanced depth of field.
Creating Depth of Field Illusions in Post-Processing
Be cautious when using apps or post-processing tools like Photoshop to artificially add depth of field effects. Manipulating focus in post can often lead to unrealistic results that break the natural laws of optics.
For example, if the foreground is blurry, followed by a sharp middle ground, then back to blurry again, it’s clear the effect was created artificially.
Key Lesson:
When creating depth of field effects, follow the rules of optics to maintain a natural look in your images.
Conclusion
Depth of field is an essential tool for photographers, offering creative control over focus and composition. By understanding the five factors that influence depth of field—focal length, distance, aperture, sensor size, and the 1/3 Rule—you’ll be able to place the depth of field window exactly where you want it. With practice, using depth of field becomes second nature.
Self-Check Quiz:
- What is depth of field?
- How does focal length affect depth of field?
- What is the Infinity setting used for?
- How does the 1/3 Rule work in depth of field?
- What are the five factors that influence depth of field?