Topic summary
Rack focus
Extracted from the Wikipedia article Focus puller.
"Pulling focus" refers to the act of changing the camera lens's focus distance to a moving subject's distance from the focal plane, or the changing distance between a stationary object and a moving camera. For example, if an actor moves from 8 metres (26 ft) to 3 metres (9.8 ft) away from the focal plane, the focus puller changes the lens's distance setting in precise relation to the actor's changing position. The focus puller may also shift focus from one subject to another as the shot requires, a process called "rack focusing".