In video, executing a smooth manual focus pull from one subject to another at a different depth primarily serves what narrative purpose?

A smooth manual focus pull, also known as a rack focus, is a cinematic technique where the plane of sharpest focus within the frame is intentionally changed from one subject to another, located at a different depth or distance from the camera, during a single, continuous shot. This process involves manually adjusting the lens's focus ring to transition the clarity from the initially sharp subject, which then becomes blurry, to the previously blurry subject, which then becomes sharp. The term "depth" refers to the relative distance of objects from the camera, creating a foreground, midground, and background. A "smooth" pull indicates a controlled, deliberate, and often slow transition, as opposed to an abrupt snap. Its primary narrative purpose is to precisely direct the audience's attention and guide their perceptio....