Screens

Movie screens look incredibly simple -- just a big rectangle of white plastic. But it turns out there is a lot of technology and design involved in their creation.

The front of the screen is smooth and white. Most screens in movie theaters have a reflective pearlescent coating that makes the screen brighter. Most movie screens also have tiny holes in them. You can't see these holes unless you get right next to the screen, but you can HEAR them. The theater puts speakers behind the screen and the holes let the sound through. In most theaters, you'll find three speakers behind the screen - one at the far left, one in the center and one at the far right. By putting the speakers behind the screen, it makes the sound seem more realistic, especially when someone is talking.

Pincushion effect

The shape of the screen also makes a difference. A flat screen is just that, a screen with no curve at all. Horizontal-curve screens curve toward the audience slightly at each end. This curving helps avoid the "pincushion effect". On a flat screen, light from the projector travels a shorter distance to reach the middle of the screen than it does to reach the edge of the screen. Since the distance to the screen controls the size of the image, this makes the image bigger at each end. By curving the ends of the screen towards the projector, the light travels the same distance after it leaves the projector.

Torex screens take this idea to the next step. Not only do they curve in at each end, they also curve in at the top and bottom of the screen creating a concave surface. On a torex screen, light from the projector should hit all parts of the screen at the same time.

Think BIG. Then go BIGGER.

Lots of museums and tourist areas have an IMAX theater. IMAX is like a normal movie theater that has been working out at the gym.

A standard IMAX theater has a huge rectangular screen. A typical IMAX screen is 16 meters high by 22 meters wide (about 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 150 feet wide. That's how big the screen is! It is many times larger than the screen at a normal movie theater.

There are also IMAX dome theaters. An IMAX dome has 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). It also enhances the feeling of motion. In fact, the feeling of motion is so strong that it makes some people ill in the same way a car, boat or plane ride can cause motion sickness.

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. 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. 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. IMAX films also play at 48 frames per second rather than 24 frames per second.

The 15/70 film size makes an IMAX projector a truly unique device. In an IMAX projector, the film is so heavy and large that a projector cannot use a claw or a sprocket to move it, and it is hard to hold such a big film frame perfectly flat for the lens. So 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.