Depth of Field

Depth of Field

noun | Camera & Optics

The range of distance in a scene, measured from the camera, within which objects appear acceptably sharp in the recorded image. Objects closer than the near limit or farther than the far limit of the depth of field appear progressively out of focus. Depth of field is controlled by three variables: aperture, focal length, and subject distance. It is one of the most fundamental creative and compositional parameters in cinematography.

Quick Reference

The Explanation: How & Why

Depth of field exists because a lens can only focus precisely on a single plane at any given focus distance. Objects on that plane are rendered as sharp points of light on the sensor. Objects in front of or behind that plane project as small circles of light rather than points -- these are called circles of confusion. When the circle of confusion is small enough to be indistinguishable from a point at the intended viewing size, the object appears acceptably sharp. The depth of field is the range within which the circles of confusion remain below this threshold.

Three variables control the size of circles of confusion and therefore the depth of field:

Aperture: The most important control. A wider aperture (lower f/T number) produces larger circles of confusion for out-of-focus objects, giving a shallower depth of field. A narrower aperture (higher f/T number) produces smaller circles of confusion, giving a deeper depth of field. This is why stopping down from T2 to T8 dramatically increases the range of apparent sharpness.

Focal length: A longer focal length produces a shallower depth of field at the same aperture and subject distance. A 100mm lens at T2 focused at 6 feet has a much shallower depth of field than a 25mm lens at T2 focused at 6 feet. This is partly due to the physics of the lens design and partly due to the fact that a longer lens is typically used closer to the subject to frame the same shot.

Subject distance: Depth of field increases as subject distance increases. At very close focus distances (macro photography), depth of field can be just a few millimetres. At far distances, depth of field extends to infinity on the far side.

Sensor size: Larger sensors produce shallower depth of field than smaller sensors at equivalent framing. A full-frame sensor at T2 has shallower depth of field than a Super 16 sensor at T2 framing the same shot, because the full-frame sensor requires a longer focal length to achieve the same field of view.

Depth of field is a primary compositional tool because it controls what the audience sees clearly and what is deliberately softened. A shallow depth of field isolates the subject from the background, directing attention and creating a visual separation between subject and environment. A deep depth of field keeps multiple planes in simultaneous focus, allowing the audience to read both foreground and background as equally important.

Historical Context & Origin

The creative use of depth of field as a compositional variable is closely linked to two opposing aesthetic traditions. Deep focus cinematography -- keeping the full depth of a scene in sharp focus simultaneously -- was developed and championed by Gregg Toland in films including Citizen Kane (1941) and The Best Years of Our Lives (1946). Toland used small apertures and wide-angle lenses to maintain focus from extreme foreground to extreme background, creating compositions in which spatial depth was used as a narrative and psychological tool. The opposite tradition -- shallow depth of field used to isolate and direct attention -- became associated with the romantic, intimate visual language of directors including David Lean and cinematographers including Freddie Young. Modern digital cinematography has strongly favoured shallow depth of field, in part because early digital video cameras had small sensors that produced deep depth of field by default, and large-sensor cameras (RED, ARRI ALEXA, Sony VENICE) were embraced partly for their ability to produce the shallow depth of field associated with film.

How It's Used in Practice

Scenario 1 -- Close-Up Isolation (DP / 1st AC): For a close-up of the protagonist during a key emotional moment, the DP sets a 85mm lens at T1.8, focused at the eyes. The depth of field at this setting on a Super 35 sensor at 5 feet is approximately 1.5 inches -- just enough to hold both eyes in focus if the actor hits their mark. The background -- a busy street -- falls into smooth, creamy defocus. The shallow depth of field removes the background as a visual distraction and places the full weight of the image on the performance.

Scenario 2 -- Environmental Context (DP): A scene requires the audience to read both a character in the foreground and a key piece of narrative information on a wall in the background simultaneously. The DP sets a 21mm lens at T8, which provides a depth of field extending from 3 feet to infinity at a 6-foot subject distance on Super 35. Both the character and the background object are sharp. The deep depth of field communicates that both elements are equally important.

Scenario 3 -- Follow Focus (1st AC): A scene involves an actor walking from 15 feet away to 4 feet from camera on a 50mm at T2.8. The depth of field is approximately 4 inches at the close position. The 1st AC builds a focus chart for the move, marking the follow focus wheel at 6-inch intervals along the actor's walk path. The pull from 15 feet to 4 feet is rehearsed four times before the take.

Usage Examples in Sentences

"At T1.4 and 85mm, the depth of field is less than an inch at this distance -- the AC needs marks for every beat."

"Stop down to T8 and put both the foreground character and the background sign in focus -- I need the audience to see both."

"The depth of field on a full-frame sensor at T2 is noticeably shallower than Super 35 at the same stop -- factor that in when choosing lenses."

"Depth of field is not just a technical parameter -- it is a decision about what the audience is allowed to see clearly."

Common Confusions & Misuse

Depth of Field vs. Depth of Focus: Depth of field is the range of object distances that appear sharp in the image. Depth of focus is a different optical concept: the range of sensor or film plane positions that produce an acceptably sharp image of a fixed object. Depth of focus is an engineering parameter relevant to lens and camera design; depth of field is the production and creative parameter. They are often confused but operate at different ends of the optical chain.

Depth of Field vs. Bokeh: Bokeh is the quality and character of the out-of-focus areas in an image -- the smoothness, shape, and colour rendering of the circles of confusion produced by a specific lens. Depth of field describes how much of the scene is sharp; bokeh describes how the unsharp areas look. A lens can produce a very shallow depth of field with unpleasant, hard-edged bokeh, or the same depth of field with smooth, creamy bokeh. Both are different aspects of lens performance and rendering.

Variations by Context

Related Terms

• Aperture -- The primary control for depth of field; wider aperture gives shallower depth
• Shallow Depth of Field -- A specific application: deliberately using shallow depth for subject isolation
• Deep Focus Shot -- A specific application: deliberately using deep depth of field to hold multiple planes sharp
• Lens -- Focal length is the second depth-of-field control after aperture
• Focus -- The specific plane within the depth of field that is rendered with maximum sharpness
• Racking Focus -- Shifting the focus point to move the sharp zone through depth during a shot

See Also / Tools

The Depth of Field Calculator calculates the exact near and far limits of sharpness for any combination of aperture, focal length, subject distance, and sensor size. For anamorphic lenses, which have different depth-of-field characteristics due to their squeeze factor, use the Anamorphic Desqueeze Calculator alongside DOF calculations.