Stereoscopic 3D – “Tool” versus “Medium”:

In the still shot from the old Alfred Hitchcock 3D movie Dial M for Murder (click for bigger image), one scene shows a plot being hatched between the two actors. What is of interest to us, is the lamp in the foreground that is out of focus. If this were a regular 2D movie, it would not be of consequence, and would in fact add to and suggest “depth” in the scene. In 3D however, it looks like a blurry mess if the audience tries to resolve the details of the carvings on the sides of the lamp or tries to see the objects on the table in front.

This brings up two interesting points.  Should everything be in focus in a 3D movie? and secondly should the use of depth-of-field, an established technique in 2D cinematography to be given equal importance as a story telling technique when used in making stereoscopic 3D movies.

Purists amongst Stereo-graphers will say yes to the first and no to the second (the vehemency of this varies with stereographers). What is alarming however, is that in the real world of Hollywood with it’s budgets and time frame constraints coupled with the existing generation of some established Cinematographers, it is hard for them to have to “un-learn” most of what was taught in 2D film school and start off with a new slate when creating stereoscopic 3D movies.

This is why one can come across statements from movie-makers stating 3D is nothing more than just another visual effects trick to be used to direct the viewers attention to where the Director wants them to look at in a scene. The argument of this article is that they couldn’t be more wrong!

Stereoscopic 3D should be treated as a whole new “medium” of story telling and is to be explored and exploited as such for creating a new genre of movie and story telling that has not been possible before.

Alfred Hitchcock’s 3D lessons:

So… if 3D is such a new ‘medium’ how was it being done mainstream since the 50′s? Back then we all know that 3D was used for the sheer gimmick factor, to draw audiences and create revenue. There was one exception… Alfred Hitchcock. His movies whether 2D or 3D always showed his talent at story telling and set him a few leagues apart from the rest.

Taking the scene above, the reason it “works” is, that 3D was used as a “medium”, NOT as a tool to tell the story. Stereoscopic 3D was used to transport the whole “set” of the movie as a virtual stage into the Cinema. Hitchcock whether knowingly or unknowingly explored the use of Stereoscopic 3D and Mise-en-scene, in what could be a new genre of effective 3D Movies.

The audience has ample time to visually “roam” the set before the main plot starts to take shape. Thereby it can be argued, that they already take in all the rich eye-candy of objects, furniture etc.. and this sets the scene for later concentration on the main plot of the movie! This is how Hitchcock could get away with blurry foreground objects, while making sure that audiences attention will be on the main characters and the plot unfolding.

Imagine a current 3D movie where the Director uses techniques such as “converge-on-focus”, thereby effectively blurring foreground and background objects (while introducing undesirable keystone artifacts) to an un-fusable mess to the eyes on a scene that has not yet been “established” (i.e the shot has just started) and contains rich visuals. This happens, and can be spotted a lot in current 3D films where 3D is being used only as a VFX tool in story telling. It gets even worse when you consider the myriad complaints about recent 2D to 3D converted movies, where the decision to use stereoscopic 3D is an after thought and done for monetary benefit.

Exploring 3D as a “medium” in storytelling:

The video clip above shows rack-focus, a common 2D Cinematic style in story telling that is used to pull the audiences attention and draw their line of sight to areas of interest in a scene. This is a dramatic effect and much needed in 2D cinema – It is also disastrous in Stereoscopic 3D.

As the Director decides when to change focus to what his/her idea of the story flow should be… if this is unleashed in a stereoscopic 3D movie, the audience could be in for a mild headache as they may still be trying to “fuse” the blurry foreground or background.

At about 50 seconds into the video there is an extremely shallow depth of field. This *can* be an effective shot in stereoscopic 3D as it is plain to see that the intention is to guide the audience either to something in the extreme foreground and then later slowly, to the background.

Converge-on-focus, the pitfalls:

Converge on focus while being easy on the eyes to converge…(we always focus on the physical screen when watching a 3D movie, true)…also leads to other unwanted side effects that need to be corrected for in post;  barrel / keystone distortion is one of them. There are more serious ones, for example the disconcerting effect of depth jumps and constant ping ponging of depth in a scene. Take off your glasses in any scene in Avatar where the humans are talking on the defence base to see this.

… in real life we do not jump 10 feet in front or 10 feet at the back to “focus” on a person talking. *THIS* is what is happening when using converge-on-focus for example, to a person at mid level depth in scene shot in a room. VERY disconcerting.

There is also the un-intentional Alfred Hitchcock “vertigo” sort of effect evident when using converge-on-focus. Example: By constantly converging on a person who is talking and moving from mid ground in a room to foreground, the depth cues get messed up, there is no sense of traversing the room from the back to the front (positive Z space to negative Z space). It also leads to “Squashed” 3D and what a good stereographer would call non-optimal use of 3D budget. Almost as good as shooting 2D and then converting it later.

Given time, audiences will no doubt be able to fuse stereoscopic 3D movie scenes rapidly, but until we reach that stage, it is wise to pre-plan shots keeping these guidelines in mind.

Understanding, un-learning and starting with a fresh slate is a benefit that the new generation of 3D movie-makers and Cinematographers will have over older players in the field who may have another hindrance to overcome; egos.  The use of Stereoscopic 3D as a medium rather than a tool in creating a new genre of movies will create that total sense of “immersion” that both movie goers and movie makers crave!

An older related post on the subject can be found here.