Intro to Depth of Field in Filmmaking

Intro to Depth of Field in Filmmaking

So you take out your DSLR, you start shooting, and you decide you want that stylistic “cinematic” look…you know, the one where only your subject is in focus and everything else falls off into a lovely blur? Well, how do you do that? The answer is depth of field. Understanding depth of field can help you change the look of your shots with ease.

What is Depth of Field?

In brief, depth of field (DoF) is the range of what is in focus in your shot. It is the distance from the nearest object in focus to the furthest object in focus within your frame. One camera setup could have multiple depths of field depending on your camera settings. A narrow (or shallow) DoF will show only a small chunk of the scene in focus. A large (or deep) DoF will show almost the entire scene in focus.

How Do You Affect Depth of Field?

There are three basic ways to affect DoF: Aperture, Distance to Subject, and Focal Length. Let’s dive in and look at each.

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Simplified illustration. Assuming your focus point and focus distance stay the same, your aperture is going to control whether you have a narrow/small or  large depth of field. However, know that distance from your subject and lens length can also affect this.

Aperture

Aperture is the opening in your lens. The wider that opening, the shallower your DoF. The smaller the opening, the larger your DoF. Look at the photo below for an example. As your lower your f-stop number (and, thus, open your aperture), the DoF shrinks. This leaves you with a “cinematic” out-of-focus background that looks great for interviews and other shots that aim to isolate a subject.

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As you increase your f-stop number and close/stop down your aperture, the DoF grows. This leaves you with a shot that has more and more of the scene in focus. These larger depths of field are great for landscape scenery.

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The aperture of a modern still photo lens is frequently controlled within the camera, normally in 1/3 of a stop increments. The change between stops is clunky and noticeable. They frequently don’t have an external iris gear at all. Cinema lenses have a separate ring for the iris, which allows for manual control. Read more about this in Photography vs Cinema Lenses: What New Videographers Need to Know.

Distance to Subject

The closer you are to your subject, the shallower the DoF. The further away, the larger the DoF, even if all your other settings stay the same. As you move your camera back, more of the scene will be in focus.

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In the example above, the camera is very close to the subject. Our DoF, as a result, is much smaller. Only one match box is in focus.

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In this example (above), the camera has moved back. Now our DoF is larger and all three match boxes are in focus. This occurred without me changing anything about my settings.

Focal Length

The focal length of your lens can make a large impact on DoF. The longer the focal length, the shallower the potential DoF appears to be. With a longer focal length lens like a 100mm, you start to have a shallower DoF than you would with a wide lens (like a 16mm) even while using the same aperture. The wider the lens, the further away the background appears to be when actually the distance between the subject and background has not changed.

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As you use longer focal lengths, it is harder to keep both the subject and the background both in focus. Usually that is what’s preferred – blur out the background and create beautiful bokeh. If you are trying to keep both the subject and the background in sharp focus you will need to use a smaller aperture. Remember that a smaller aperture is actually a larger number, such as f/16. A larger aperture is a smaller number, such as f/2. Read more about this in How Lens Length Affects Apparent Background Size: An Example Using the Moon.

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Why is Depth of Field Important?

Understanding DoF will make a huge difference in your photography and filmmaking. Let’s say, for example, that you’re a landscape photographer and you want a beautiful wide shot of a city. You need to know how to se tup your camera to ensure everything is in focus and looks just right. After having read this article, you now know some of the steps: close your aperture down, move back from the subject, and toss on a wide lens. That will give you as large a DoF as possible quickly.

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As a rule of thumb, the larger the sensor, the more shallow the depth of field can appear. For example, the depth of field of an image shot with a lens set to f/2.8 on a full frame camera will be more shallow looking than an image shot with a Super 35mm sensor camera with the same lens that’s also set to f/2.8. Read more about this in Sensor Size and Filmmaking: Choosing the Right Camera for Your Project.

The alternative is true for a shallow DoF. If you want to isolate a subject, you’ll want to move closer, open your aperture, and grab a longer lens. Knowing how to manipulate your camera to get the DoF you want is critical for a filmmaker.

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Kellan Reck is a video editor and cinematographer for the Boston Red Sox, producing and building content for the team's social media platforms and Fenway Park's video boards. This work with the team has awarded Kellan four New England Emmy Awards. Additionally, Kellan runs a YouTube channel where he shares tutorials, tricks, and more that help other filmmakers develop their skills. Enjoy a new video every Wednesday at 10 AM!

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