Shifting focus during the shot — from foreground to background or vice versa. Directs the viewer's attention deliberately and demands a skilled focus puller.
The focus puller turns the focus ring during the ongoing shot — that is racking focus. It's not the camera moving, nor the actor shifting into the light: the plane of focus actively travels from one object to another. This sounds simple, but it is one of the most technically demanding tasks on set, because every millimeter off means the entire shot is lost.
The classic application: Two actors sit opposite each other at a table. The camera is positioned to the side. While the first actor speaks, the focus is on them — the second actor is blurred behind them. When cutting to the reaction shot, the focus puller racks the focus to the second actor. This only works if they know the exact distance, have the lens focal length in mind, and can anticipate the actors' movements. Modern digital cameras are less forgiving than film — the depth of field is narrower, especially at wide apertures like T/2.8 or T/2.0. A centimeter or two off, and the viewer sees that the focus is incorrect.
Practical on set: The focus puller measures before each setup with a steel ruler or an ultrasonic rangefinder. They mark the critical positions on the focus wheel with chalk or tape — one mark for the starting point, one for the endpoint. During the take, their finger glides at a steady pace between these marks. For fast rackings (e.g., in action scenes or with surprised glances), a fluid, decisive movement is required. For slow rackings — when the camera is pulling and the focus is moving simultaneously — the movement must be imperceptible, calibrated to the speed of the camera movement.
Racking is also a narrative device. It directs the viewer's gaze without needing to cut. In conversations between two people, the rack follows the line of sight or reinforces an emotional shift: first, we see the liar in focus, then the focus shifts to the skeptical reaction of the other. This is subtler than a cut and creates a different tension — especially in thrillers and dramas.