Perspective Tricks

Okay, one last time.
These are small, but the ones out there are far away.

Father Ted, “Hell” (1996)
Graham Linehan, Arthur Mathews

I was recently reminded of Father Ted explaining perspective to Father Dougal (is it really more than twenty years ago?) when I happened on a bit of art under the Tay Road Bridge. The pillars that support the approach roads have been painted in patches of bright colour, like this:

Tay Bridge Mural 1
Click to enlarge

Motorists on the underpass shoot past this with just a flicker in their peripheral vision. But if you go and stand in the right place, and get the columns aligned in just the right way, you see this:

Tay Bridge Mural 2
Click to enlarge

That’s neat, isn’t it? I really wanted the direction in which the word SOUTH is revealed to be, well, south; but it’s closer to south-west. The geometry of the pillars makes it impossible to do the trick on a north-south axis. Curiosity made me walk down to the other end of this area, to stand next to the door that gives access to the pedestrian walkway on the bridge above, and sure enough there’s a NORTH as well, though one inconveniently placed pillar makes it impossible to see the whole word:

Tay Bridge Mural 3
Click to enlarge

But that inconvenient pillar at least supports a plaque with the artistic credits and a bit of history:

Tay Bridge Mural Plaque
Click to enlarge

And one of the “unused” pillars (blocked from view by the “R” in NORTH, above) supports a portrait of William Fairhurst, the designer of the bridge:

William Fairhurst, Tay Bridge Mural

Now, to get those two words spelled out evenly on columns that are very different distances from the viewer, the artists needed to do a trick with perspective—the nearby letters are much smaller than those farther away. If you take a look at my first photograph, you’ll see that the “UT” of SOUTH occupies about a third of the column height, while the “S” takes up about three-quarters of its column and even spills on to the ceiling.

So, as Father Ted might explain: big things far away look just like small things nearby.

This perspective effect is exploited in an optical illusion called the Ames Room, after its inventor, ophthalmologist Adelbert Ames, Jr.

Ames realized that you could make a trapezoidal room look like a rectangular one, if you made a distant corner taller than a closer corner, and confined the viewer’s position by making them look through a peep-hole. Once you’ve set up the illusion (and perhaps made it more compelling by including trapezoidal windows, doors and floor tiles), anyone who stands in the room will seem to vary in height, according to whether they stand in the far corner (in which they look small in proportion to the height of the room), or the near corner (in which they look taller).

Here’s a classic photograph of how it looks when three men of similar height line up along the far wall of an Ames Room:

Ames Room
(Notice how the position of their feet reveals that they’re actually standing on a sloping floor.)

And here’s the geometry of the illusion, as seen from above:

Geometry of an Ames Room

You can get a better feel for the three-dimensional shape of an Ames Room from this video demonstration  by neuroscientist Vilayanur S. Ramachandran, which featured in the BBC’s special-effects documentary The Computer That Ate Hollywood (1998):

Ramachandran suggests that the illusion is maintained by the fact that we’re used to seeing rectangular rooms, and there’s some support for that point of view from the fact that people who live in a less “carpentered world” (and therefore rarely encounter rectangular rooms) are less susceptible to the illusion. *

But you don’t need the whole room—even quite simple visual cues can create an Ames Room effect. A couple of cue objects of appropriate visual size, combined with an apparent horizontal alignment, will do the trick. This visual trickery was used frequently in Peter Jackson’s Lord Of The Rings films, to make the hobbits appear smaller than the humans. For instance, here is Elijah Wood (playing the hobbit Frodo) apparently sitting side by side on a cart with Ian McKellen’s Gandalf, as seen in the film:

Frodo and Gandalf

And here’s the real shape of the cart:

Ames cart from Lord Of The Rings

Jackson’s special effects engineers even managed to create an “Ames Room” that adjusted itself to maintain the illusion as the camera position changed:

The actors not only had to deliver their lines while looking past each other, but while they, along with parts of the set, were moving around on a platform as the camera moved.

So that’s how you make something look small by pretending it’s closer than it actually is. The reverse technique was also frequently used in film-making—making something look huge by pretending it’s farther away than it actually is. It was a common trick, in the days before CGI, to place a model in the foreground that was merged with live action in the background.

For example, here’s a classic scene from Steven Spielberg’s Close Encounters Of The Third Kind (1977)—the discovery of the lost ship S.S. Cotopaxi in the Gobi Desert:

Cotopaxi in the Gobi, Close Encounters of the Third Kind

The ship is actually a detailed model, a few metres long, and the people, camels and helicopters are several hundred metres beyond it—the smooth featurelessness of the intervening sand makes the distance impossible to judge.

And then there’s the trick of making something look far away by building it smaller than normal. That could be as simple as tapering the width and height of a fake street built on a sound stage, to give the impression that it extends farther into the distant than it actually does. But the classic example of this technique appeared in the background of the final scene of Casablanca (1942):

Final scene, Casablanca

That aeroplane parked on the tarmac behind Claude Rains, Humphrey Bogart and Ingrid Bergman is a Lockheed Electra 12A—or at least, a half-scale model of one, built from wood and cardboard. The people who are seen walking around the aircraft were all adults of short stature, hired specifically to give a misleading scale to the plane, to make it look farther away than it actually is. And the implausible “Casablanca mist” serves to conceal the fact that the whole scene was shot indoors, with just enough room for the scaled-down aircraft.

Finally, symmetry suggests I should have a category for “making something look closer by building it larger than normal”. For some reason, there doesn’t seem to have been any cinematographic demand for that technique …

* V. Mary Stewart. A Cross-Cultural Test of the “Carpentered World” Hypothesis Using The Ames Distorted Room Illusion International Journal of Psychology 1974; 9: 79-89

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