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What is IMAX?

(Pocket-lint) - The IMAX system was first introduced to find a way to project films to a bigger size than ever before without losing any of the quality. Instead of 35mm, it uses 70mm film with 15 perforations per frame and it requires special IMAX film cameras that can feed tape that size in order to record onto it. You also need IMAX projectors which run the film laterally past the bulb instead of in the vertical plane as with a normal cinema film projector. Each frame is held in a registered position on the reel and the film is held tight to the first element of the lens by a vacuum as it passes the projector bulb. This is to ensure that there is no shake or judder and that the movie stays in razor sharp focus at all times. The resulting picture is designed to fill the whole of the human visual field, which gives it its name of IMAX short for “image maximum”.

How are the IMAX cinemas different?

The screens are normally much bigger than those of traditional movie theatres. The standard size is 22 x 16.1m for a total of 354m squared but the largest in Darling Harbour, Sydney, is eight stories high and around 10 times larger than a regular cinema, covering a total area of 1,015 square metres. The screens are usually curved in order to surround the viewer to a small degree and always perforated, with thousands of holes to let the sound come through from the speakers set on the scaffold behind. The screen is made of a vinyl stretched over the structure and painted silver in order to reflect polarised light often used in 3D films.

Some IMAX theatres are round structures with elliptical shaped screens. These are known as IMAX Dome or OMNIMAX and use the same technology plus the addition of a fish-eye lenses to put the film into proportion when projected onto the curved surface.

The IMAX film projectors offer approximately eight times better resolution than normal 2K projectors using two 15,000W bulbs as compared to 35mm ones in the region of 2000-4000W. These quartz crystal lamps are filled with xenon gas at 25 atmospheres of pressure, so full body armour is required when handling or changing them as the fine shards would be lethal if the bulb was dropped with that kind of force inside it. The heat generated during operation creates an enormous cooling challenge requiring 1600 cubic metres of air and 36 litres of distilled water running through the lamp housing every minute.

The projector itself weighs an enormous 1.8 tonnes and the lenses are twice the height of the film so that a pneumatic piston can shift the stock up or down during presentation if any dust gets in the way. The lens also has its own wipers to remove any foreign bodies.

The projector is in no way responsible for playing the audio as none of the sound is embedded on IMAX film unlike 35mm stock. The idea is to leave as much room on the print to let the image be as large as it can be. Instead the film is synced with six separate tracks that come on three simultaneously playing CDs which accompany the film.

Can any film by shown at an IMAX cinema?

Well, yes and no. Only 70mm prints can be run through the IMAX projector and that film can only be recorded onto with special IMAX cameras. However, 35mm films can be transferred onto IMAX film but most will be properly upgraded to avoid loss in picture quality. Some non-IMAX films are shown at IMAX cinemas using either DLP or traditional 35mm projectors and these will only take up a small portion of the IMAX cinema screen.

Is IMAX the same as 3D?

No. Most 3D films will be played at IMAX theatres and you'd expect the majority of the features shown in these places to be 3D, but the two are not necessarily linked. Many 3D films are shot on 3D IMAX cameras which have two lenses set at 64mm apart to represent the average distance between the human eyes. The upcoming Tron: Legacy has been shot on 3D IMAX cameras and will be shown in 3D at IMAX cinemas but the recent The Dark Knight shown in IMAX was only shot on standard IMAX cameras and so was only in 2D. 3D IMAX cameras weigh 113 kg/250lbs. Not the most portable of devices. Not really built for handheld work or small crews.

What about IMAX Digital?

The digital version of the format started rolling out in 2008. There are currently two IMAX Digital cinemas in Europe - both in the UK. They don't use the traditional 70mm IMAX projectors but instead work with 2 x 2K DLP projectors. This is significantly lower resolution than the approximately 8K you get from 70mm film IMAX and has been one of the major complaints of this iteration along with the smaller screen size of 8.5 x 17.5m. Naturally, it's much less expensive for the cinemas but often ticket prices are the same as normal IMAX screens anyway. The process is no different at the recording end as there are no IMAX Digital cameras.

How long has IMAX been around?

The first IMAX films were 30-45 minute factual pieces often commissioned by councils, tourist attractions and museums for impressing and educating visitors but since James Cameron's full length documentary on IMAX - Ghosts of the Abyss, set around the wreck of the Titanic and the stories around the legendary ship - there has been a boom in feature films with 10-15 each year, either shot on or digitally remastered for IMAX screens.

Is it any good?

Yes. IMAX cinemas add a pretty jaw dropping level of immersion and largely, the experience is very well received. IMAX is very often the best place to watch 3D films as the format works best in as big a frame as possible and that's exactly what these screens provide. That said, not all IMAX cinemas are set up perfectly and there have been some complaints that projections have slipped off the edge of the screen and that visually, 2D IMAX films are not significantly better than those shown at normal cinemas.

Where is my nearest IMAX theatre?

There are 320 IMAX cinemas in 42 countries all over the world. Half of these screens are in the US but there are six in the UK - three in London (Waterloo, Wimbledon & Greenwich) and one in Glasgow, Birmingham and Bradford.

Enjoyed this article about 3DTV? Then check out more articles in our 3DTV week on the 3DTV homepage.

Writing by Dan Sung. Originally published on 16 April 2013.
Sections TV