IMAX theatre technology is, quite possibly, the most advanced theatre technology on the face of Earth. Six- to eight-storey screens with the most immense surround sound systems make IMAX an incredibly rich movie experience.

The Screen

Spanning from one wall to the other, and from the floor to the ceiling, it's hard to tell where the screen ends once the film starts - that's how huge it is. Hidden behind the screen are at least six or more massive 24-inch speaker cabs that are the key element in IMAX's surround sound system; whatever's supposed to be making a sound in the movie (a person talking, a machine), with IMAX, it really does sound like the noise is originating from that source.

At an IMAX film, many people recommend sitting in the middle of the super-slanted theatre - in that position, you see more of the picture and less of the frame. Unfortunately, most people know this. Get near the front of a line if you want a chance at this choice seating!

The Sound

The sound in a standard IMAX theatre is better than the image in believability, fidelity and precision. True, the fidelity and precision are hard to beat, but the sound is incredible. As stated previously, using a six-channel sound system, chock-filled with 24-inch (and bigger) woofers (bass speakers), huge subwoofers mounted into the floor and behind the screen, and equally large mid-ranges and tweeters (high speakers), not only will the sound never break up, but if you were to close your eyes during an IMAX film, you'd be tempted to think you were there. The sound is recorded digitally - three CDs per film, which are synchronised to the film by computer - a departure from the normal analogue method used in most films

The Film

IMAX film is something again. Consider this:

• Camcorder film is 8mm measured diagonally
• Typical photographic film is 35mm measured diagonally
• Typical movie film is 70mm measured diagonally
• IMAX film is ten times the area of 35mm, and about three times the area of 70mm. Its dimensions are around 70mm by 70mm

Incredible. Then consider that it's being projected onto a screen that's probably 20m tall - which, coincidentally, puts it at about 35m from corner to corner - and considering that we know the image is incredibly high-fidelty at that distance, consider how fine an image you'd see if you took a peek at the moving images displayed upon this massive screen...

The Projector

The IMAX projector is another piece of art in science. It uses something they call 'rolling loop film movement'. Translation? Rather than feed the film vertically, as they do in 70mm projectors, the IMAX film is fed horizontally. It's fed through a number of rollers and capstans, then vacu-sucked up against the lens, and positioned absolutely perfectly so that you'll get the best and most static in image focus and position. The projectors themselves are massive - and all closed-in.

The bulb's a lot brighter, too - up to one third brighter, and if it looks a third brighter, that means that the bulb is actually about 10 times brighter- you gotta love logarithmic brightness sense.

The History

The IMAX theatre was created by three men - Graeme Ferguson, Roman Kroitor and Robert Kerr - for Montréal's EXPO 1967. EXPO already used megascreen theatres, but those theatres used several projectors to show the image. IMAX uses a single, huge projector to have the entire image displayed. This gives it numerous advantages:

• Uniform position
• Uniform focus
• Uniform brightness
• Uniform film speed
• Uniform position in the film

In the mid-1950s, a similar technology was developed, called Vista-Vision. Vista-Vision used 35mm film, run horizontally through the projector, similar to how today's green-screening and older blue-screening technology operates. The beauty of IMAX is that its massive film, rather than using a 3:8 aspect ratio (such as is used in movie 70mm film), it uses a 3:4 aspect ratio - just like your television.

IMAX in 3D

If you want to see anything in 3D, you need two images. Any creature that can see has at least two eyes. Virtual reality helmets offer two slightly different images. IMAX 3D films with two cameras, and thereby projects with two images.

Now, 3D film has been around for a while, but this 3D doesn't use cardboard 'glasses' with a red and a blue filter. Oh no. IMAX 3D uses modern technology to offer us image depth. Each lens in the projection is polarised (passed through a special transparent filter), and then the glasses you wear have matching polarised lenses. The left lens receives only the information sent by the left projector, and vice versa. This polarisation effect makes it pretty odd when you look at someone else who's wearing the glasses. Normally their eyes are 3D - not anymore.

Fun IMAX facts

• If you were to put a big log directly in front of an IMAX projector, it would spontaneously combust.

• On average, 12.7kg (28 pounds) of garbage is collected after each IMAX show.

• A typical 2D 45-minute IMAX film is 4.5km (3 miles) long.

• If you were on the Moon and someone turned on an uncovered IMAX projector bulb, you could see it with the naked eye. After all, the bulbs put out 15,000 watts.

• The word IMAX is derived from Maximum Image.

• OMNIMAX (or IMAX Dome) screens can be up to 30m (99 feet) in diameter.

• IMAX film is strong - it could be used to pull a truck.

Important Links

IMAX Technology database
IMAX's official list of IMAX theatres around the world