What's the big deal about IMAX films? Just about everything, as it turns out, from the whopping frame size to monster screens, giant projectors and film "platters" as big as the top of a dining-room table.

And that's only part of the technology behind the scenes of two new movies in the area this month.

A few days ago, "Olympic Glory" -- a briskly paced 2-D look at the 1998 Winter Games in Calgary -- began a six-month run at the Maryland Science Center. Two weeks from today, Oct. 27, the Smithsonian Institution will host the premiere of "Galapagos," a super-lush, 3-D adventure about biology research in the remote Pacific islands 700 miles west of Ecuador.

"Olympic Glory" is the first film licensed by the International Olympic Committee. "Galapagos" is the first 3-D project sponsored by the Smithsonian's National Museum of Natural History (NMNH). Both chose the IMAX format. Why?

The answer lies in the ways that IMAX films that have been carefully designed to have a mega-impact on your brain.

High, Wide and Handsome

Even by modern standards, IMAX screens are humongous. The one at NMNH's Samuel C. Johnson Theater is 66 feet high and 90 feet wide -- about the same height as a six-story building and about one-third as long as a football field. It's nearly as big as the largest such screen in the western hemisphere, the 80-by-100-footer at the Sony IMAX theater in New York.

The goal is to make the image so big that it extends to the edge of your field of vision in all directions. That way, you feel more like you're "in" the movie and less like you're in a theater. Moviemakers started doing that in the 1950s by using new techniques such as Cinerama and CinemaScope that allowed a wider screen.

Until then, the standard movie image was one-third wider than it was tall -- that is, it had an "aspect ratio" of 1.33 to 1, or 4 to 3, exactly what IMAX uses. But audiences responded so well to the wider screen that the American standard evolved into the current 1.85 to 1.

IMAX theaters have higher screens. But they also have seats placed at a steeper angle. That puts the audience closer to the projected image so that it can look up and down as well as from side to side.

In addition, NMNH's vinyl screen, which weighs nearly half a ton, is painted with a special reflective metallic coating to make the image somewhat brighter than most commercial screens. Like all modern movie screens, it is perforated to allow sound to travel from the battery of speakers behind the screen.

Because of the high screen, IMAX projector lamps must be ridiculously bright. The laws of physics demand that, if you double the amount of screen area, you need four times the light.

Like many other systems, IMAX uses bulbs filled with a neon-like gas called xenon. When you run electric current through it, it gives off radiation that is very close to natural sunlight and rich in blue hues needed for color film.

Nobody likes changing the 15,000-watt, water-cooled lamps, made of quartz and filled with pressurized gas. "We wear full flak jackets when installing the lamps," says Bridget M. Shea, NMNH theater manager. "The quartz will explode periodically with enough force that the glass imbeds itself in the metal housing of the projector."

Of course, when you project patterns from a transparent piece of film onto bigger and bigger areas, the risk of fuzziness increases. IMAX technology has several ways to minimize that effect.

For one thing, the film size is far larger than anything else you're likely to see. An individual frame is about the size of a baseball card, a rectangle 70 millimeters, or 2.75 inches, long. That's 10 times the area of frames used in ordinary 35mm movies and three times the area of other modern 70mm film prints, usually enlargements from a 35mm original.

IMAX is not the first system to film subjects on large negatives. It was tried as early as 1929, and in 1955, the "Todd-AO" wide-screen process, using 70mm prints, debuted with the movie "Oklahoma."

IMAX uses the entire frame for the picture. By contrast, a run-of-the-mill, 35mm movie uses only about two-thirds of the film frame for the image. The rest is either blank or contains the sound track.

Of course, IMAX movies have full six-channel sound. But it's recorded on a completely separate tape or CD system, which then is computer-synchronized with the film projector.

The IMAX projector keeps a tight focus by using a vacuum to suck the film flat against the lens elements. And there's a lot of film on those big platters -- a little more than two miles' worth shoots through the projector in 40 minutes, the typical IMAX film length, at about 5.6 feet per second. In an ordinary commercial movie, the same amount of film would last about 100 minutes.

In a regular movie projector, the film moves vertically. In IMAX, it moves horizontally at the industry standard speed of 24 frames per second, just enough to give the film-strip series of still images the illusion of smooth motion.

New IMAX projectors, including the one at NMNH, also can handle 48 fps for state-of-the-art "high-definition" movies.

Just Shoot Me

Because of the frame size, an IMAX camera's film cartridge lasts only about three minutes, compared with 11 or 12 for an ordinary 35mm camera. So it can take quite a while to shoot even a short movie. NMNH's 40-minute "Galapagos" took 14 weeks of filming with two 3-D cameras.

A loaded IMAX 3-D camera weighs 228 pounds and takes 30 minutes to reload. Otherwise, it generally resembles other high-tech 3-D cameras, which use basically the same technology that your brain does to achieve a three-dimensional effect.

You see the world in 3-D because your nervous system can process incoming visual information from each eye separately.

True, your eyes are only two to three inches apart. But even that small difference means that each eye sees the same scene from a slightly different angle, especially for things closer than 12 feet. The effect is large if an object is close, small if it's far away.

The brain uses the difference between signals received from each eye to determine the distance, depth and shape of objects in your visual field, ultimately blending the two into a combined 3-D image that is, in effect, the movie of your life projected onto consciousness. It's called binocular vision.

The big challenge for 3-D filmmakers is to create a theatrical illusion of depth on a screen that is absolutely, two-dimensionally flat. How do they do it?

First, they must shoot two separate negatives. That involves using either two cameras or one camera with two lenses spaced about 2.5 inches apart, just like human eyes.

Thus, the movie actually consists of two different 12,000-foot spools of film, one for the left eye and one for the right, rolled up horizontally on two large flat platters. Both strips are fed into the projector simultaneously.

The projector also has two lenses and projects both left- and right-eye images onto the screen at the same time. So far, so good. But how is each of your eyes supposed to know which image it is supposed to see and which it can to ignore?

Most solutions involve ways of blocking your left eye from seeing the right-eye material, and vice versa. The old-fashioned method used colored glasses with one red and one blue (originally green) lens. The outlines of objects projected on the screen were outlined with red or blue, depending on which eye was supposed to interpret that perspective.

A far superior system, and the one used at NMNH for "Galapagos," takes advantage of a 1932 invention by Edwin Land -- the polarizing filter.

Light is a wave that, like all waves, vibrates in a certain plane. Nearly all light rays you encounter in everyday life are jumbled, with their individual waves vibrating in many random directions or "polarities." A polarizing filter lets only one of those polarities pass.

Battling Glare

For example, Polaroid-type sunglasses cut the amount of light that enters your eyes because their lenses are composed of thousands of tiny vertical, slit-like divisions. As a result, the lens is transparent only to light vertically polarized -- that is, light that vibrates in a straight up-and-down plane. Nothing else makes it through.

This is a swell way to cut down on glare. When light strikes a lake or the hood of your car, it tends to be horizontally polarized because the lake surface or hood top is horizontal. So vertically polarized lenses eliminate the worst kinds of glare.

The same technology is used in "Galapagos" and many other IMAX 3-D films. Each lens of the projector sends its beam through a polarizing filter. The beam intended for one eye is vertically polarized; the one for the other is horizontally polarized. When you look at the screen without equipment, you see two slightly out-of-alignment images.

But when you put on special polarizing glasses, the images suddenly appear to jump off the screen in full 3-D. That's because the lens covering the left eye lets in one polarity and completely screens the other; the right eye lens does just the opposite.

Each eye receives only its own distinct and separate images. The brain processes the two signals and interprets the results as three-dimensional depth and shape.

Other IMAX formats use a headset in which each eye is covered with an independently controlled liquid crystal lens. A signal on the screen alternately blanks your left and right eyes dozens of times a second, achieving the same kind of 3-D effect.

Those headsets, which also feature an added sound channel, are harder to sanitize between showings, however. Polarizing glasses aren't a snap but are easier.

NMNH's Johnson theater facility contains a commercial dishwasher unit of the sort used in a busy cafeteria. After each showing, the used glasses are run through the dishwasher, virtually eliminating the chance of, say, getting somebody else's cold by handling previously used glasses.

When showing 2-D IMAX movies such as "Mysteries of Egypt," the Johnson theater seats 487. For 3-D movies, however, managers close 60 seats too far to either side to give the audience a good three-dimensional effect.

For information on the Johnson theater schedule, call 202-633-7400. Admission to "Galapagos" is $6.50 for adults and $5.50 for children and senior citizens. Groups of 25 or more must call 202-633-9045 or 1-877-932-4629 for reservations.

Admission to the Maryland Science Center is $10.50 for adults, $9 for seniors and $7.50 for children 4 to 12. Call 410-685-5225 for information.

3-D Projector

Two projection lenses, one for the right eye display, and one for the left.

Four film platters, outgoing and incoming for the right-eye display and the left. The large film flies across the room from the reels to the projector. This requires that the projection room be extremely clean at all times.

3-D Camera

The camera weighs 228 pounds loaded, and film canisters can hold only enough for three minutes of footage. Changing the canisters takes 30 minutes. The camera has two lenses for capturing right- and left-eye movies at the same time.

All-New 3-D Glasses

Polarizing lenses are used to control which eye sees which film frames. The beam intended for one eye is vertically polarized; the one for the other is horizontally polarized.

The right-eye display . . .

. . . and the left . . .

. . . produce 3-D images, merged inside your brain.