Focus & Depth

Focus is how a cinematographer points. Everything sharp invites the audience to explore the image; one thing sharp tells them exactly where to look and refuses them everything else.

Two frames comparing deep focus, where all three planes are sharp, with shallow focus, where only the middle figure is sharp Deep focus Shallow focus
Same blocking, opposite instruction to the audience. Deep focus trusts you to explore the frame; shallow focus isolates one person and makes the rest of the world a suggestion.

The types of focus

Deep focus
Foreground, midground and background all sharp at once. Deep depth of field allows action in all three planes simultaneously, which suits blocking and staging chaotic scenes. The famous example is Citizen Kane (1941, DP Gregg Toland), where characters in the far background comment on the action in the foreground inside a single frame.
Shallow focus
Only a specific plane is sharp; the rest blurs away. Achieved with a wide aperture (low f-stop) to create a narrow depth of field. It isolates a character from their world and forces attention. Moonlight uses shallow depth of field throughout to bring an extreme level of intimacy to Chiron's emotional journey.
Rack focus pull focus
Shifting the focus point from one subject to another during a shot: one element blurs as another sharpens. It connects two subjects without a cut: a character in the foreground and a figure appearing in the doorway behind them.
Follow focus
The focus puller continuously adjusts focus to keep a moving subject sharp. Not an effect, a craft: the audience should never notice it happening.
Soft focus
The whole image is slightly blurred, giving a glow or haze. It needs a special lens with this "defect" or a filter. In the old days crews stretched nylons across the lens or wiped it with vaseline. Used for dream sequences and flashbacks to give a nostalgic glow, as Spielberg did throughout A.I. Artificial Intelligence.
Split diopter
A half-lens attachment creating two separate shallow focal planes in one shot, so something close and something far can both be sharp. Look for the faint blurry line dividing the frame. Brian De Palma and Quentin Tarantino use it often, including in The Hateful Eight.
Tilt-shift
Tilts the plane of focus so only a thin diagonal strip is sharp, making real scenes look like miniatures or dreams. Roger Deakins used it for the bar mitzvah scene in the Coen Brothers' A Serious Man, visualising Danny's marijuana-influenced perspective.
Focus in / focus out defocus
The whole image drifts in or out of sharpness: a soft transition between scenes, or a character losing consciousness.
Rack focusSharpness travels between planes inside one unbroken shot.
Split diopterNear and far both sharp, joined by a faint seam.
Tilt-shiftA thin sharp band; the world reads as a miniature.
Soft focusEverything hazed. Memory, dream, nostalgia.
Rule

Depth of field is a sentence about attention. Deep focus says "the world matters as much as the person." Shallow focus says "nothing outside this face exists right now." Choose the one that matches what the scene is about, not the one that looks more expensive.

Watch

Depth of Field Explained: Ultimate Guide to Camera Focus (StudioBinder, Ep. 4). Reference: Types of Camera Focus in Film.

Cinematography & Mise-en-Scène cheat sheets · built from The Foundations of Cinematography and Mise-en-Scène.