What is Z-axis defocusing?

Rack focus shooting, also known as pull focus, requires a short depth of field. This means that at the same time, only the narrow space along the Z axis is in a clear focus range. When the camera moves the focus, he/she moves the focus from one focal plane to another. When shifting focus, the audience's attention shifts from objects in one focal plane to objects in another focal plane. By using a short depth of field, the built-in "special effects" (in? The camera effect allows us to selectively guide the audience's attention at any time in the scene. The following is the use of shifting focus in the key scene at the end of the second act of the film "The Graduate".

Movie example: The Graduate

Ben, the leading actor in his twenties, just came home from college. This time, he had sex with a friend of his parents, Mrs Robinson. The problem is that Ben soon fell in love with Mrs Robinson's daughter Elaine.

At the end of the second act, Ben hurried to Elaine and confessed to her. He broke into her parents' house and found Elaine in the bedroom upstairs. Before he could tell Elaine, Mrs Robinson's footsteps came. Elaine faces Ben, with her back to the open bedroom door at the back. When Ben began to explain why the identity of the old woman was important, Elaine's mother appeared at the door (Figure 3).

Mrs Robinson is at the door facing the station. Elaine can't see her mother. Mrs Robinson is vague, like a ghost. When Elaine turned around and the focus shifted to Mrs Robinson, Elaine was out of focus (Figure 4). Every wrinkle on Mrs Robinson's face was revealed. After a while, Mrs Robinson disappeared from the door. When Elaine turned to Ben, her face remained blurred for a while, showing her inner confusion. After she thought about it, the focus shifted to her face.

In this scenario, shifting focus has two functions:

A) Reveal one's identity, in this case, the identity of an "old woman"-Mrs. Robinson. By shifting the focus, Mrs Robinson answered Elaine's puzzled questions with her own body.

B) Before paying attention to Elaine, wait for her to think clearly and let her understand her confusion.