Dolly zoom

A computer-generated representation of a dolly zoom

A frame from an animation showing a dolly zoom being performed. At the top of the image is the camera's view; the cubes stay the same size as the teapots in the background grow bigger. At the bottom of the image is a plan view showing the camera moving back while zooming in, illustrating how the effect is achieved.

Dolly zoom effect can be seen in the big video, while in the smaller the camera does not zoom, and the object moves with the camera. the FOV does not change thus, there is no dolly effect

The dolly zoom is an in-camera effect that appears to undermine normal visual perception.

The effect is achieved by zooming a zoom lens to adjust the angle of view (often referred to as field of view, or FOV) while the camera dollies (moves) toward 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 angle is pulled away from a subject while the lens zooms in, 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.

The visual appearance for the viewer is that either the background suddenly grows in size and detail and overwhelms the foreground, or the foreground becomes immense and dominates its previous setting, depending on which way the dolly zoom is executed. 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, often with strong emotional impact.

The effect was first conceived by Romanian cinematographer Sergiu Huzum, but was first used by Irmin Roberts, a Paramount second-unit cameraman, in Alfred Hitchcock's film Vertigo.

In addition to Vertigo the shot has been used in many films, including Goodfellas, Road to Perdition, Jaws, Body Double, The Island of Dr. Moreau, Josie and the Pussycats, and Mike and Dave Need Wedding Dates.^[1]

Alternative names

A dolly counter zoom is also variously known as:

Focus disturbance zoom
A "zido"
A "zolly"
The "Hitchcock zoom" or the "Vertigo effect"^[1]
"Hitchcock shot" or "Hunter shot"^[2]^[3]
Triple Reverse Zoom
Reverse Tracking Shot
Back Zoom Travelling
Hunter Smith Shot
"Smash Zoom" or "Smash Shot"
A "Jaws shot"
Vertigo zoom
Telescoping
Trombone shot
Push/pull
The Long Pull
The Trombone Effect
A Stretch shot
Reverse Pull
More technically as forward zoom / reverse tracking or zoom in / dolly out
Trans-trav (in Romanian and Russian), from trans-focal length operation and travelling movement
Contra-zoom

Purpose of the effect

The dolly zoom is commonly used by filmmakers to represent the sensation of vertigo, a "falling-away-from-oneself feeling" or a feeling of unreality, or to suggest that a character is undergoing a realization that causes him or her to reassess everything he or she had previously believed. After Hitchcock popularized the effect, he used it again for a climactic revelation in Marnie.

Optics

For most purposes, it can be assumed that the image space and the object space are in the same medium. Thus, for an object in focus, the distance between the lens and image plane $s_{\text{i}}$ , the distance between lens and the object $s_{\text{o}}$ , and the focal length $f$ are related by

{1 \over s_{i}}+{1 \over s_{o}}={1 \over f}.

Then the transverse magnification is

M={s_{\text{i}} \over s_{\text{o}}}={f \over (s_{\text{o}}-f)}.

The axial magnification $M_{\text{ax}}$ of an object at $s_{\text{o}}$ is the rate of change of the lens–image distance $s_{\text{i}}$ as the lens–object distance $s_{\text{o}}$ changes. For an object of finite depth, one can conceive of the average axial magnification as the ratio of the depth of the image and the depth of the object:

M_{\text{ax}}=\left|{d \over d(s_{\text{o}})}{s_{\text{i}} \over s_{\text{o}}}\right|=\left|{d \over d(s_{\text{o}})}{f \over (s_{\text{o}}-f)}\right|=\left|{-f \over (s_{\text{o}}-f)^{2}}\right|={M^{2} \over f}.

One can see that if magnification remains constant, a longer focal length results in a smaller axial magnification, and a smaller focal length in a larger axial magnification. That is, when using a longer focal length while moving the camera/lens away from the object to maintain the same magnification M, objects seem shallower, and the axial distances between objects seem shorter. The opposite—increased axial magnification—happens with shorter focal lengths while moving the camera/lens towards the object.

Calculating distances

To achieve the effect, the camera needs to be positioned at a certain distance from the object that is supposed to remain still during the dolly zoom. The distance depends on how wide the scene is to be filmed and on the field of view (FOV) of the camera lens. Before calculating the distances needed at the different fields of view, the constant width of the scene has to be calculated:

{\text{distance}}={\frac {\text{width}}{2\tan \left({\frac {1}{2}}{\text{FOV}}\right)}}.

For example, a FOV of 90° and a distance of 2 meters yield a constant width of 4 meters, allowing a 4-meter-wide object to remain still inside the frame during the effect.

References

1 2 Wickman, Forrest (January 21, 2014). ""The Evolution of the Dolly Zoom," in One Supercut". Slate.
↑ Norman Holland. "Hitchcock's Vertigo: One Viewer's Viewing".
↑ "The "Vertigo shot" and the oneiric frame".

External links

Vertigo Effect article on TV Tropes

Field size

Camera placement

Perspective Over-the-shoulder Point-of-view (POV) Reverse Trunk Single / multiple-camera setup

Camera angle	Tilt Aerial High-angle Bird's-eye Crane shot Jib / boom shot Low-angle Worm's-eye view Dutch angle

Camera movement

Lens effects

Focus
- Racking
- Depth of field
- Shallow
- Deep
Zooming

Other techniques

Special effects

Practical	Prosthetic makeup Animatronics Puppetry Creature suit Miniature effect (hanging) Pyrotechnics Aerial rigging (Wire-flying) Squib Matte painting Sugar glass Theatrical blood

In-camera	Tilted plane focus Forced perspective Schüfftan process Dolly zoom Lens flares Lighting effects Filtration Shutter effects Time-lapse Slow motion Fast motion Speed ramping Bipacks Slit-scan Reverse motion Front projection Rear projection Multiple exposure Infrared photography Bullet time

Visual	Computer-generated imagery Split screen Stop motion Go motion Chroma key Compositing (digital) Optical printing Introvision Smallgantics Match moving

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