How IMAX Works

By: Marshall Brain

People watch IMAX 3D film Avatar in theater
IMAX screens are sized to fill your field of vision. China News Service / China News Service via Getty Ima

If you have ever been to an IMAX theater and seen an IMAX movie, then you know that IMAX is an experience -- a much different experience than you get in a normal theater. IMAX is so different and so unique that it is nearly a genre of its own.

In this article, we'll look at both the technology and the process of IMAX. The technology includes the theaters themselves and the projectors, while the process involves the steps that a production company must go through to create an IMAX film. We'll interview Michael Lewis, who has co-produced the IMAX film "T-REX: Back to the Cretaceous," and produced and financed "Siegfried and Roy: The Magic Box," two of the most popular IMAX films ever created, to learn about the special challenges of this amazing medium!


The IMAX Experience

Layout of an IMAX dome
Layout of an IMAX dome

As soon as you walk into an IMAX theater, the difference in this format is immediately obvious -- the screen is gigantic! There are two different types:

  • IMAX theaters - A standard IMAX theater has a huge rectangular screen. A typical IMAX screen is 16 meters high by 22 meters wide (approximately 52 by 72 feet), but they can be much larger. The largest IMAX screen is 30 meters (98 feet) high. Imagine standing next to an eight-story apartment building that is wider than it is tall. That's how big the screen is! It is many times larger than the screen at a normal movie theater.
  • IMAX domes - An IMAX dome provides a hemispherical screen that wraps the entire theater. Domes can be up to 30 meters in diameter.

Whether you are in a theater or a dome, the effect is amazing. The screen is large enough to fill your field of vision. By doing this, the screen gives you an incredible feeling of immersion (there is nothing outside the film to distract your attention), and it also enhances the feeling of motion. In fact, the feeling of motion is so strong that it makes some people ill.


In order to fill this gigantic screen with a clear picture, IMAX films are shot and printed on huge film stock that is completely unique in the industry.

IMAX film stock is about 10 times larger than 35mm film stock.
IMAX film stock is about 10 times larger than 35mm film stock.

Most films that you see in a theater come in a 35-millimeter format. The frame is 35 millimeters wide, and nearly square. But movie screens are not square -- they are very wide for their height. So the wide image is compressed into the 35-millimeter frame and expanded by the projector to fill the screen.

Some theater films come in a 70-millimeter format. This format provides roughly double the resolution, and the frame is naturally the width of the screen so there is no compression.

IMAX film is called the 15/70 film format. Each frame is 70 millimeters high and 15 perforations wide. In other words, the film size is about 10 times bigger than standard 35-millimeter film. This film size gives an IMAX movie incredible clarity, even on the huge screens in IMAX theaters.

The 15/70 film size makes an IMAX projector a truly unique device. If you have read How Movie Projectors Work, you understand the basic mechanism of a 35mm projector:

  • The film feeds in from the top of the projector.
  • A claw or sprocket arrangement advances the film one frame and holds it steady in front of the light.
  • A shutter opens and lets light shine through the film and lens onto the screen for a fraction of a second.

In an IMAX projector, the film is so heavy and large that a projector cannot use a claw to move it, and it is hard to hold such a big film frame perfectly flat with respect to the lens. Therefore, an IMAX projector is completely different from a normal projector:

  • The film moves through it horizontally rather than vertically.
  • A vacuum system sucks each image onto a piece of glass in front of the lens so that the image is oriented perfectly in front of the lens.
  • The shutter opens for a longer period of time than on a normal projector in order to let more light through. The bulb for the projector is a 15,000-watt, water-cooled xenon unit.

All of this advanced technology means that an IMAX projector weighs over 2 tons (1,800 kilograms) -- the equivalent of a small car! That's what it takes to get such a bright, clear image onto such a tremendous screen.

IMAX Innovations

Since its debut, IMAX has been pushing the envelope to create the most realistic, immersive film experience possible. Several of the innovations introduced in select IMAX theaters include:

  • Dome technology - allows the image to wrap completely around your peripheral vision
  • 3-D technology - IMAX uses both polarized glasses and LCD shutter technology to display very intense 3-D films.
  • 48 frames per second - This is double the standard frame rate and greatly increases visual detail.
  • Advanced sound systems - IMAX theaters use a 6-channel sound system, and in some theaters you also wear a headset that provides two extra sound channels for each viewer.
  • Digital Remastering - IMAX DMR converts a 35mm frame into digital form at a high resolution, extracting the important image elements to create a crystal clear form of the original photography.

By combining all of these advanced features, IMAX theaters create the most realistic and intense movie experience around.


Making an IMAX Film

Movie poster for "T-REX"
Movie poster for "T-REX"
Photo courtesy IMAX

Watching an IMAX film is an amazing experience, but the process of creating an IMAX film is even more amazing. For a variety of reasons, IMAX film production is much more complex than normal film production. To understand the process, we spoke to Michael Lewis of L-Squared Entertainment, who co-produced "T-REX" and produced and financed "Siegfried and Roy," two popular IMAX 3-D films.

Movie poster for "The Magic Box"
Movie poster for "The Magic Box"
Photo courtesy IMAX

Both of these films are especially interesting from a production standpoint. Not only are the films shot on IMAX's 15/70 film stock, but they are also shot in 3-D and make extensive use of computer-generated (CG) effects.


Because of the screen size and incredible detail on an IMAX image, the quality of computer-generated effects must be perfect to work on an IMAX screen. For example, the dinosaurs in "T-REX" have five times the detail of the dinosaurs in the "Jurassic Park" movies. This means that it takes five times more computer power to render each "T-REX" image, and five times the storage space.

According to Lewis, one of the key challenges when making any IMAX film has to do with the film size. The size of the film means three things to a director:

  • The camera is immense. It weighs 240 pounds (109 kg), so it requires special supports and rigging to move it around. A typical 35-mm movie camera, by comparison, weighs only 40 pounds (18 kg).
  • The size of the film means that the camera can hold only a three-minute spool, and it takes 20 minutes to reload.
  • The incredible detail available with a film size this large means that everything about the shot must be perfect, and each image must be stunning. The audience sees every flaw, and a lackluster image totally wastes the potential of the IMAX medium.

According to Lewis, "The cost and complexity in every segment of physical production is an order of magnitude greater with IMAX." In addition, "There are only two IMAX 3-D cameras in the world, so if you have a breakdown, you are standing around spending $100,000 a day on production costs."

An IMAX camera and crew at a movie shoot
An IMAX camera and crew at a movie shoot
Photo courtesy IMAX

On a normal film, 10 setups a day is normal. With IMAX, "Three or four a day is moving at lightspeed", according to Lewis. The camera is also very noisy -- it sounds like a chain saw when it is running. Actors and crew are all affected by the noise. In "Siegfried and Roy," the animals also reacted to the noise. All of the audio has to be done in post-production because of the camera's noise on the set.

Animals react to the noise and excitement at movie shoots.
Animals react to the noise and excitement at movie shoots.
Photo courtesy IMAX

The screen size and clarity mean that every frame of an IMAX film must be perfect. "In 35 millimeter, you can use lots of cheats in visual effects -- things like rain and darkness," says Michael Lewis. "In IMAX you see everything, and everything is photo-real. There are 100+ IMAX screens in museums, so things must be as accurate as possible. With a dinosaur, you have to worry about things like nostril slant and tooth decay. When placing a dinosaur on the ground, the eye instantly knows if something is not perfect."

The technical challenges mean that an IMAX film, which is normally just 40 or 50 minutes long, costs just as much to make as a normal film for theatrical release. For example, the "T-REX" film took five months for a feasibility study to prepare for filming, 40 days for the shoot and then 12 to 13 months to complete the film in post-production. The CG effects and dinosaurs consumed approximately 4 terabytes of disk space.

A typical IMAX film's production costs fall somewhere in the range of $3 million to $8 million for a 2-D feature, and $8 million to $15 million for 3-D, with 3-D films involving CG running at the high end of the scale. Films can either be funded by IMAX or self-funded by studios like Michael Lewis' L-Squared Entertainment.

Despite the challenges, the unique experience of the IMAX theater makes IMAX films a compelling medium for directors. With the number of theaters increasing worldwide, and with a rapidly growing audience for the IMAX experience, it is likely that a wide variety of films will be created for this venue in the years to come.

For more information on IMAX and related topics, check out the links on the next page.