If you have watched film and television you have probably seen the dolly zoom. It’s when the foreground element stays the same size while the background elements grow or shrink.
It goes by all sorts of different names such as the The Reverse Tracking Shoot, Zolly, the Stretch Shoot, Forward zoom Reverse Tracking, Trombone Shot, Contra-Zoom, Telescoping… or The Vertigo Effect.
In fact it was Alfred Hitchcock who first implemented this technique in his 1958 film Vertigo. According to legend Alfred Hitchcock got this idea when he fainted at a party. It was a Paramount second unit cameraman Irmin Roberts who developed it with Hitchcock for the film Vertigo.
Since Vertigo, the Dolly Zoom has been used in many other productions – including by Hitchcock himself in Marnie. Steven Spielberg utilized this effect in Jaws in 1975 in a sudden distortion of perspective isolates and zeroes in on Chief Brody – his worst fears have become true.
The Dolly Zoom was also used in Martin Scorsese’s 1990 film Goodfellas. Near the end of the film, in a conversation between Ray Liotta and Robert Deniro where everything seems normal on the surface, the dolly zoom emphasizes the world is slowly changing around them. Henry Hill has come to the realization that his best friend has just put a hit on him and there really are no goodfellas in a life of crime.
Why Does it Work?
It all boils down to the basics of photography – we’re taking a 3 Dimensional World and reducing it down to 2.
Let’s imagine a Camera Obscura – a pinhole camera. We have a subject, an aperture and an imaging plane. The light rays from the subject travel through the aperture in straight line and onto the imaging plane. We if we draw a straight line from each edge of the image plane through the aperture we get an angle. This is our field of view.
With a pinhole camera, there’s no way to increase or decrease our field view without moving the image plane.
But we can use lenses with different focal lengths (or zoom power) to bend the light. Now we can see more of what’s around- get a wider field of view or zoom closer to get a narrower field of view.
By bending the light we introduce a phenomenon called perspective distortion which is the warping of objects based on the distance from the camera.
Perspective distortion does not change by simply increasing or decreasing the focal length or zoom. If you sit in one spot and zoom in you won’t notice and shifting of perspective. But it does change based on the relative position of the camera to the subject.
And this is how the magic of the Dolly Zoom works: We increase the focal length (zoom in) as we simultaneously move the camera out or vice versa. The zoom keeps the frame crop the same so the foreground stays the same through out the move – this isolates the effect of the perspective distortion caused by the dolly motion so we see that shifting of perspective.
Dolly Zoom in Production
Theory is all well and good but it takes a bit of effort to actually get a decent dolly zoom in production. You’re going to need two things – a dolly and a zoom – that should be obvious.
You can try to do it on a slider but you might run into the problem of having the slider in your shot and that’s not good.
As far as the zoom goes – you really need to have a camera with a smooth zoom preferably a motorized servo controlled zoom. It’s nearly impossible to pull it off with a photograph lens zoom. After all, that’s why it took till 1958 to achieve the effect – they needed smooth mechanics to pull it off.
To demonstrate I have a cut of the maestro himself – Mr Hitchcock. I’ll start the shot dollied all the way in and zoom out. I’ll keep the aperture stopped down so I get a deep depth of field so I’m not fighting with focus during this move.
Now as I pull the dolly out, I will zoom in at the same time trying to match the speed of the zoom with the speed of my dolly.
Now if I want the opposite effect, I’ll dolly in from here while zooming out. Either way, I like to start with the dolly all the way in to get an idea of what zoom I want to start with or end with.
Getting this effect takes a lot of practice to get just right as the speed which you need to dolly will change depending on where you are in the focal length range. Just keep doing the shot over and over again untill you get it right – just know that it takes a bit of time.