Audiovisual split focus

Star Trek: The Motion Picture (1979)
Star Trek: The Motion Picture (1979)

In this article, I want to introduce the idea and technique of split focus. In cinematography, the concept of split focus was explored mainly during 1970’s to the early 1980’s, namely by Brian De Palma and Robert Wise.

But even to this date, this technique is still used, probably as homage to these directors. Interestingly, the concept of split focus can also be found in sound (more in the examples below).

What always interests me is the narrative motivation for specific concept or technique, so here are 3 possible narrative motivations for the use of audiovisual split focus:

  • to introduce multiple elements without editing
  • to intensify the viewer’s emotional response
  • to add sense of realism

To discuss this technique in more detail, we have to briefly introduce/remind few facts about depth of field (DOF).

Depth of Field (DOF)

Depth of field (DOF) is a great and very powerful tool how to direct or guide the audience where to look at, i.e. how to tell them what is important in the image.

If you look at the image below, your attention most probably goes to the girl, which is in focus.

The Enigma by Andrew Mohrer
The Enigma by Andrew Mohrer

Technically speaking, DOF is the distance range in the image along the Z axis that appears acceptably sharp (=area perceived as being in focus). Although the lens can truly focus only at one distance (plane) along the Z axis, the transition between area in focus and out of focus is gradual; therefore we can talk about “field” (instead of plane).

In cinematography, a large DOF is often called deep focus (think Orson Welles and Citizen Kane) and a small DOF is often called shallow focus (think Gus van Sant and Paranoid Park).

Unfortunately, things are little bit more complicated than this; DOF is influenced mainly by the aperture of the lens: Larger aperture produces shallow focus, while small aperture produces deep focus.

But at the same time, aperture controls how much light hits the film or digital sensor, so you have to find the balance between DOF and exposure by:

  • some kind of compensation (additional light for small aperture, ND filters for large aperture)
  • using optical tricks
  • using a device called split field diopter.

Split field diopter

Star Trek: The Motion Picture (1979)
Star Trek: The Motion Picture (1979)

With the invention of split field diopter, it is possible to achieve the look and feel of deep focus (=large DOF) without the need of using additional lights (to compensate for the small aperture).

A split diopter is half convex glass that attaches in front of the camera’s main lens to make half the lens nearsighted. The lens can focus on a plane in the background and the diopter on a foreground element. (1)

A split diopter does not create real deep focus, only the illusion of this. What distinguishes it from traditional deep focus is that there is not continuous depth of field from foreground to background. Because split focus diopters only cover half the lens, shots in which they are used are characterized by a blurred line between the two planes in focus.(1)

Note: The following text consists of excerpts taken from the article “Notes on the split-field diopter” by Paul Ramaeker, available after free registration at jstor.org.


The split-field diopter lens simply permits focusing on a very close object on one side of the frame, while a distant subject is photographed normally through the uncovered portion of the prime lens; in this way, the shot may be focused on both near and far subjects simultaneously.

Star Trek: The Motion Picture (1979)
Star Trek: The Motion Picture (1979)

The split-field diopter, while it could not provide true deep focus, could create an impression of considerable depth, without the requirement of any additional light. Previously, such effect was only feasible by combining two separate shots in an optical printer via a matting process.

While the edge of the glass at the split between the diopter portion of the lens and the flat glass is invisible, the diopter part itself has an extremely shallow depth of field. As a result, the region where the lens is split, in the center of the frame, will appear blurred due to the focal differences between the diopter and the prime lens. In order to maintain the illusion of depth and obscure the use of the diopter, this focal difference must be hidden in some way.

Star Trek: The Motion Picture (1979)
Star Trek: The Motion Picture (1979)

For example, the edge of the diopter lens may be positioned so that it lines up with a straight edge in the background – such as the corner of a room, the edge of a column or a bookcase. A neutral background, of uniform color and texture, may hide the split, but may not always be feasible.

Two examples from Dressed to Kill, 1980

Dressed to Kill (1980)
Dressed to Kill (1980)

Unbeknown to either detective Marino or Dr. Elliott, Peter (the young man sitting outside) is bugging the conversation inside detective’s office. The staging and use of split field diopter functions here to unite a disparate group of characters variously connected to a woman’s death and to denote their differential access to narrative information.

Dressed to Kill (1980)
Dressed to Kill (1980)

Peter times exits from Dr. Elliott’s office so as to judge what sort of delay to put on the camera he is hiding at the scene.


Other Examples

Reservoir Dogs (1992)
Reservoir Dogs (1992)
Equilibrium (2002)
Equilibrium (2002)
The Untouchables (1987)
The Untouchables (1987)
Pulp Fiction (1994)
Pulp Fiction (1994)
Valibation (2013)
Valibation (2013)

 

Blurry line between audio and visuals

By now you’ve probably noticed the blurry line between the two areas in focus. Well, the same blurry line can be found between audio and visuals. These two guys have more in common than you might think.

My favorite example is when Walter Murch talks about editing in relation to Beethoven’s music or when Janusz Kaminski talks about shutter angle and describes actor’s movement using musical term.

One of the most recent examples of the correlation between audio and visuals is when Phil Benson is discussing the balance between music, sound effects and dialogue at the Sundance Film Festival. To quote Phil Benson:

“Imagine if you could have shallow DOF with like 4 different areas on the screen, your audience wouldn’t know what to focus on […], so imagine sound as being somewhat similar in some ways to playing with DOF, visually.”

Now, we know that split field diopter enables us to have two subjects simultaneously in focus at different distances along the Z axis. In other words, it creates two separate DOFs and the look and feel of deep focus (=large DOF). And I was wondering, what would be the equivalent in sound?

Club scene in Social Network

The Social Network (2010)
The Social Network (2010)

There is an amazing scene in Social Network, where Mark Zuckerberg meets Sean Parker in a club called Ruby Skye. It’s essentially a business meeting happening in the loudest possible environment.

There is this incredibly loud music firing from the speakers and at the same time, there is a dialogue happening between Mark and Sean.

Visually, try to think of this scene as a scene with deep focus (=large DOF). Both the foreground element (dialogue) and background element (music) are in focus.  Except there is no visible blurry line between them :-).

In this scene, loud music adds to the sense of realism – we are in the club, people have to shout to hear each other! Second reason for having such loud music is that, to paraphrase Ren Klyce, David Fincher wanted to achieve that feeling of being Mark Zuckerberg completely overwhelmed, he has never been to club. (2)

Final words

This article serves more or less as an introduction to visual thinking about sound.  I hope that it sparked some ideas! Writing about DOF in relation to sound was really exciting and this type of article is definitely not the last one on CINEMA SHOCK!

References

  1. http://en.wikipedia.org/wiki/Depth_of_field
  2. http://soundworkscollection.com/videos/socialnetwork

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