Dolly-Zoom or Hitchcock Shot: JAWS
The dolly zoom is an unsettling in-camera special effect that appears to undermine normal visual perception in film.
The effect is achieved by using the setting of a zoom lens to adjust the angle of view (often referred to as field of view) while the camera dollies (or moves) towards or away from the subject in such a way as to keep the subject the same size in the frame throughout.
In its classic form, the camera is pulled away from a subject while the lens zooms in (lens length increases) or vice versa. Thus, during the zoom, there is a continuous perspective distortion, the most directly noticeable feature being that the background appears to change size relative to the subject.
As the human visual system uses both size and perspective cues to judge the relative sizes of objects, seeing a perspective change without a size change is a highly unsettling effect creating a highly emotional impact.
The visual appearance for the viewer is that either the background suddenly grows in size and detail overwhelming the foreground; or the foreground becomes immense and dominates its previous setting, depending on which way the dolly zoom is executed.
The effect was first developed by Irmin Roberts, a Paramount second-unit cameraman, and was famously used by Alfred Hitchcock in his film Vertigo.