eyestilts: faq

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What's a telestereoscope?

A telestereoscope is a device that increases the distance between your eyes. This has the effect of enhancing your depth perception. It makes things seem more three-dimensional than they normally would. In some cases, it can seem to shrink the world down to miniature models. One person described it as "like looking at the real world through a Viewmaster".

Why did you build it?

Lots of reasons. For fun. To give people a drug-free way to alter their reality. To make the world, literally, a smaller place.

Where'd you get this crazy idea?

The idea came from two places at once: thinking about stereo photography, and going to Burning Man for the first time in 1999.

My friend Jeff's dad, a major stereo photography buff, once showed me a stereo picture of the Grand Canyon. It was shot with two cameras about ten feet apart. The effect was weird: it looked very three-dimensional alright. But it also looked too small, as if someone had built a very perfect scale model the size of a city block.

Then I went to Burning Man, and had the opposite experience. The Black Rock Desert, and the city growing in the middle of it, were just too big. It was impossible to gauge the distance of things: without the clues that normally surround us, like buildings and trees, I found I just couldn't wrap my head around it all. What looked like a little tent from far away would, after a half hour walk, turn out to be a gigantic dome. It was disorienting, sometimes in a good way, sometimes not.

This got me thinking about size, and scale, and perception. I remembered the Grand Canyon photo, and suddenly it was clear what I had to do.

How does it work?

The device itself is very simple. It consists of two periscopes, one for each eye. Each periscope is made of a pair of mirrors. The periscopes shift the eyes upwards and out to either side.

The principle behind it is based on human visual perception. In order to make sense of your visual surroundings, part of what your brain must do is estimate how far away things are. One of the ways your brain does this is by using the relative disparity between the images projected onto the retinas of your two eyes. Each object in your field of view will project to a slightly different location on each retina. Essentially, the closer the object, the greater that difference will be. Your brain already knows how far apart your eyes are (about two or three inches), and using that information it can make a good estimate of exactly how far away each object is. This is also the principle behind 3-D movies and stereograms.

Now, if you artificially exaggerate this relative disparity by placing your eyes several feet apart, your brain, still believing that your eyes are only two inches apart, will come to the wrong conclusion about how far away things are. This incorrect information about depth then interacts with everything else you know about what you're seeing (that is a tree, that is a car, etc.) and you begin to draw strange conclusions about the size of things. In short, because it's hard to believe that your head is really ten feet wide, you are forced to conclude that the world around you is really small.

Is this a new invention or what?

Not really. I designed my first prototypes without knowing anything about the long history of telestereoscopy. It's such a simple idea, it turns out it's been invented lots of times. Psychologists and neurologists have used similar devices to study depth perception in experiments, or to show a slightly different scene to each eye (in which case it's called a haploscope). The folks at the Exploratorium built one once, which they gave the catchy title "Wide Eyes". Filmmakers use them while making 3-D movies, to determine how far apart to place the cameras for maximum effect. Sailors use them to estimate the distance to land. And in the military, engineers have attached them to night-vision goggles, to help soldiers see their targets. A wide range of uses, indeed.

What is it made of?

It's made of steel, with glass mirrors.

How did you build it?

I built the first rickety prototypes out of wood on a workbench in my dining room. Later, Chris Whitney saved me from my ineptitude as a carpenter and brought me to his metal shop, where we set about designing the scale prototype and eventually the full-size device. Chris did most of the metalwork, which included sawing, plasma-jet cutting, drilling, tapping, grinding, and both MIG and TIG welding, and I supported him with filing, burnishing, design work and math. For more detail, see the project diary.

I tried it and it didn't do anything. What's wrong with me?

Probably nothing. A small percentage of people (about 4%, or so I've read) for one reason or another do not have stereo vision. For example, kids born with a lazy eye will not develop stereo vision unless they get corrective surgery by a very young age. But even among people with full stereo vision, there is a wide range of sensitivity to the information obtained from relative disparity. If it did nothing for you, you're probably just on one end of that scale.

I tried it and it gave me a headache. What's wrong with you?

Oops. We must not have adjusted the mirrors properly that day. Please accept our apologies!

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