Dolly zoom is a shot in which the camera dollies toward or away from a subject while zooming in the opposite direction, distorting space.
The dolly zoom — also called a contra-zoom, trombone shot, or simply 'the Vertigo effect' — is created by physically moving the camera while simultaneously adjusting the zoom in the opposite direction. The result is that the subject stays the same size in the frame while the background appears to expand or compress, producing an unsettling sense of dislocation. Alfred Hitchcock and cinematographer Irmin Roberts devised the technique for 'Vertigo' (1958) to visualise the protagonist's acrophobia. Steven Spielberg deployed it on the boardwalk in 'Jaws' (1975) at the moment Chief Brody realises a child has been eaten. Martin Scorsese, Peter Jackson, and Robert Wise have all used it. Once a rare special effect, it has become shorthand for psychological vertigo — the visual equivalent of the floor giving way.