3D doomed to fail

In a letter to Mr Roger Ebert, Hollywood sound engineer and editor Walter Murch explains why 3D cinema will never succeed–at least, so long as it's used in screen projection.

The biggest problem with 3D, though, is the "convergence/focus" issue. A couple of the other issues -- darkness and "smallness" -- are at least theoretically solvable. But the deeper problem is that the audience must focus their eyes at the plane of the screen -- say it is 80 feet away. This is constant no matter what.


But their eyes must converge at perhaps 10 feet away, then 60 feet, then 120 feet, and so on, depending on what the illusion is. So 3D films require us to focus at one distance and converge at another. And 600 million years of evolution has never presented this problem before. All living things with eyes have always focussed and converged at the same point.


If we look at the salt shaker on the table, close to us, we focus at six feet and our eyeballs converge (tilt in) at six feet. Imagine the base of a triangle between your eyes and the apex of the triangle resting on the thing you are looking at. But then look out the window and you focus at sixty feet and converge also at sixty feet. That imaginary triangle has now "opened up" so that your lines of sight are almost -- almost -- parallel to each other.


We can do this. 3D films would not work if we couldn't. But it is like tapping your head and rubbing your stomach at the same time, difficult. So the "CPU" of our perceptual brain has to work extra hard, which is why after 20 minutes or so many people get headaches. They are doing something that 600 million years of evolution never prepared them for. This is a deep problem, which no amount of technical tweaking can fix. Nothing will fix it short of producing true "holographic" images.

How tall is it?

I've been saying this ever since I studied perspective at university.  Human beings use the parallax effect between their two eyes to judge distances up to 20 feet.  Beyond that, the eyes are parallel, so depth perception then relies on visual cues such as perspective, the relative height of objects, light, and haze.  This is why forced perspective works.  By, for example, changing the sight lines of a stage set you can make it appear much larger than it actually is.  Since your eyes can't verify the distance, your brain relies on angles and relative sizes, so it thinks that what it sees is larger.  Indeed, this is the trick that Disney uses to make Sleeping Beauty's Caslte look much taller than the 77 feet it actually is.

It's also the reason why 3D films never look convincing, are tiring, and often make people feel sick.  In addition, I don't know about other people, but I can't even see the effect unless I concentrate on it.  As for 3D televisions, I've seen them and I wouldn't take one as a gift.  Since this is the case, I prefer to save the extra couple of quid and stick to the 2D versions.

When they get around to developing stereovision tanks, I'll reconsider.

Update: Broken link repaired.