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IMAX Theater

Educational films in vivid detail on a very large screen.

IMAX/OMNIMAX theaters are great educational destinations. IMAX guests enjoy films presented on an intensely large screen (often one or two stories tall) in great detail. Films presented are usually documentary in nature and can be an excellent educational experience.

IMAX (for Image Maximum) is a film projection system created by IMAX Corporation that has the capacity to display images of far greater size and resolution than conventional film display systems. A standard IMAX screen is 22 m wide and 16 m high (72.6 x 52.8 ft), but can be larger. IMAX is the most successful large-format special-venue film presentation system.

A variation of IMAX, IMAX Dome (originally called OMNIMAX), is designed for projection on tilted dome screens.

Precursors

The desire to increase the visual impact of film has a long history. Cinemascope and VistaVision widened the projected image from 35 mm film, and there were multi-projector systems such as Cinerama for even wider presentations. While impressive, Cinerama was cumbersome, difficult to set up, and the joins between the screens were difficult to hide.

Technical aspects

The intent of IMAX is to dramatically increase the resolution of the image by using much larger film stock at a resolution of 38720 x 24120. To do this, 70 mm film stock is run "sideways" through the cameras. While traditional 70 mm film has an image area that is 48.5 mm wide and 22.1 mm tall (for Todd-AO), in IMAX the image is 69.6 mm wide and 48.5 mm tall. In order to expose at standard film speed of 24 frames per second, three times as much film needs to move through the camera each second.

Drawing the large-format film through the projector was a difficult technical problem to solve; conventional 70 mm systems were not steady enough for the 586x magnification. IMAX projection involved a number of innovations.

William Shaw of IMAX adapted an Australian patent for film transport called the "rolling loop" by adding a compressed-air "puffer" to accelerate the film, and put a cylindrical lens in the projector's "block" for the film to be vacuumed up against during projection (called the "field flattener" because it served to flatten the image field). Because the film actually touches the "field flattener" lens, the lens itself is twice the height of the film and is connected to a pneumatic piston so it can be moved up or down while the projector is running, this way, if a piece of dust comes off the film and sticks to the lens, the projectionist can switch to the clean side of the lens at the push of a button. The lens also has "wiper bars" made of a felt or brush-like material which can wipe the dust off the lens as it moves up or down to keep the show vivid.

IMAX projectors are pin-stabilized, meaning 4 registration pins engage the sprockets at the corners of the projected frame to ensure perfect alignment. Mr. Shaw added cam-controlled arms to decelerate each frame to eliminate the microscopic shaking as the frame "settled" onto the registration pins.

The projector's shutter is also open for around 20% longer than in conventional equipment and the light source is brighter. The largest 12-18 kW xenon arc lamps have hollow, water-cooled electrodes. An IMAX projector is therefore a substantial piece of equipment, weighing up to 1.8 tons and towering at roughly the size of a kitchen refrigerator. The xenon lamps are made of a thin layer of quartz crystal, and contain about 25 atmospheres of xenon gas. Because of this, projectionists are required to wear protective body armour when changing or handling these lamps because the flying shards of crystal could be deadly when combined with the high pressure of the gas within.

IMAX uses a stronger "ESTAR" (Kodak's tradename for DuPont's Mylar) base. The reason is not for strength, but precision. Developing chemicals do not change the size or shape of Estar, and IMAX's pin-registration (esp. the cam mechanism) is intolerant of either sprocket-hole or film-thickness variations. The IMAX format is generically called "15/70" film, the name referring to the 15 sprockets per frame of 70 mm stock. The bulk of the film requires large platters rather than conventional film reels.

IMAX film does not include an embedded soundtrack in order to use more of the image area. Instead the IMAX system specifies a separate six-channel 35mm magnetic tape synchronized to the film. (This original system--35mm mag tape locked to a projector--was commonly used to "dub" or insert studio sound into the mixed soundtrack of conventional films.) By the early 90's, a separate digital 6-track source was synchronized using a more precise pulse-generator as a source for a conventional SMPTE timecode synchronization system. This development presaged conventional theatrical multichannel sound systems such as Dolby Digital and DTS. This digital source came in the form of of a unit called a DDP (Digital Disc Playback) in which the soundtrack was recorded onto multiple cd-rom discs which would play the sound which was recorded to the discs as a digital audio file. This DDP system has been replaced in almost all theaters with the newer DTAC (Digital Audio Theater Control) system which utilizes a computer running the IMAX's proprietary DTAC software. The software works in a similar style as the DDP except that instead of the audio file being based on discs, it is instead played directly off a hard drive in the form of a single uncompressed audio file containing the 6 channels which are distributed directly to the amplifiers rather than using a decoding method such as Dolby Digital.

Further improvements and variations on IMAX include several 3-D presentation methods and the possibility of a faster 48 frames per second rate (known as IMAX HD, this system was installed in one theater as an experiment, but was deemed too costly and abandoned). Improvements in the sound systems have included a 3D sound system and the elliptical-pattern speaker-clusters.

IMAX theater construction also differs significantly from conventional theaters. The increased resolution allows the audience to be much closer to the screen; typically all rows are within one screen-height. (Conventional theaters seating runs 8 to 12 screen-heights) Also, the rows of seats are set at a steep angle (Up to 23 degrees in some domed theaters) so that the audience is facing the screen directly.

IMAX Dome/OMNIMAX

The frame layout of the IMAX Dome film.

In the late 1960s, the San Diego Hall of Science (now known as the San Diego Space and Science Foundation) began searching North America for a large-format film system to project on the dome of their planned 76-foot tilted-dome planetarium. One of the front-running formats was a double-frame 35mm system, until they saw IMAX. The IMAX projector was unsuitable for use inside a dome because it had a 12-foot-tall lamphouse on top. However, IMAX Corporation were quick to cooperate and was willing to redesign their system. IMAX designed an elevator to lift the projector to the center of the dome from the projection booth below. Spectra Physics designed a suitable lamphouse that took smaller lamps (about 18 inches long) and placed the bulb behind the lens instead of above the projector. Lights of Canada developed a fisheye lens that would project the image onto a dome instead of a flat screen.

The new system, that the San Diego Hall of Science called OMNIMAX, uses a fisheye lens on the camera that squeezes a highly distorted 180 degree field of view onto the 70mm IMAX film. The lens is aligned below the center of the frame and most of the bottom half of the circular field falls beyond the edge of the film. The part of the field that would fall below the edge of the dome is masked-off. When filming, the camera is aimed upward at an angle that matches the tilt of the dome. When projected through a matching fisheye lens onto a dome, the original panoramic view is recreated. OMNIMAX wraps 180 degrees horizontally, 100 degrees above the horizon, and 22 degrees below the horizon for a viewer at the center of the dome. It premiered in 1973 at the Reuben H. Fleet Space Theater and Science Center in San Diego's Balboa Park.

IMAX has since renamed the system IMAX Dome. Even though the Reuben H. Fleet Science Center – which coined the original name – now uses the new name, many theaters still call it OMNIMAX.

OMNIMAX theaters are now in place at a number of major American museums and also at several major theme parks and Las Vegas hotels, but it seems likely to remain a novelty experience rather than a widespread commercial phenomenon. Relative to their size, OMNIMAX theaters have small seating capacity and are very expensive to build and maintain. Museums are able to run the theaters at a profit only because they are able to subrogate the construction expenses through grants and public fundraising and then show relatively inexpensive documentary films. In this way, OMNIMAX theaters have become a "cash cow" for financially strapped public institutions.

IMAX 3D

To create the illusion of 3 dimensions, the IMAX 3D process uses two camera lenses to represent the left and right eyes. The two lenses are separated by an interoccular distance of about 64 mm/2.5 in., the average distance between a human's eyes. By recording on two separate rolls of film for the left and right eyes and projecting them simultaneously, we can be tricked into seeing a 3D image on a 2D screen. The IMAX 3D camera is a very cumbersome camera, weighing over 113 kg/250 pounds. This makes it extremely difficult to film on-location documentaries such as the Space Station 3D film. (Space is a popular subject for the IMAX 3D format.) The IMAX screen, averaging at 8 stories tall, is the perfect medium for 3D movies to be shown on. Not only does the large negative format allow for pristine quality images, but the massive screen and close viewing distance provides a very immersive experience for the audience.

There are two methods to creating the 3D illusion in the theatre. The first involves polarization. During projection, the left and right eye images are polarized perpendicular to one another as they are projected onto the IMAX screen. By wearing goggles with lenses polarized in their respective directions to match the projection, the left eye image can be viewed only in the left eye since the polarization of the left lens will cancel out that of the right eye projection. Another method for 3D projection involves headsets that contain electronic liquid crystal shutter (E3D) lenses. The lenses are synced to the twin projectors that alternate rapidly between left and right eye images at 96 frame/s to project one image at a time on the screen that is momentarily viewed by the appropriate eye by allowing that eye's lens to become transparent while the other remains opaque.

One particular problem that 3D movies face is that the 3D effect does not extend past the boundaries of the physical screen. It is for this reason that the screen must be large enough to cover as much of the viewer's peripheral vision as possible. Another problem with IMAX 3D movies is due to an inherent difference between our eyes and the film format. Because of the large negative, depth of field is dramatically reduced, causing an often distracting depiction of the scene. Computer-generated imagery films do not have this problem as they are able to control the depth of field in the images to allow everything to be in focus. While some may argue that this is less artistic than regular 2D films that purposefully employ shallow depth of field for aesthetic reasons, the IMAX 3D experience is a much more immersive one than regular 2D films, and therefore the viewer can be disoriented by seeing images that are out of focus – a natural side-effect of the 3D experience.

Viewer experience

For the viewer, these technical differences result in a much more immersive, engaging experience than conventional film projection. The large screen and close seating mean that much of the viewer's field of vision is filled with the image, and the high resolution and positional stability of the film format imparts a sense of reality and detail. IMAX film can be overwhelming at times, with some viewers experiencing motion sickness during scenes with significant motion, especially if the action cuts between moving and still scenes.

Content

Although IMAX is an impressive format from a technical perspective, its popularity as a motion picture format has traditionally been limited. The expense and logistics of producing and presenting IMAX films has dictated a shorter running time compared to conventional movies for most presentations (typically around 40 minutes). The majority of films in this format tend to be documentaries ideally suited for institutional venues such as museums and science centers. IMAX cameras have been taken into space aboard the Space Shuttle, to Mount Everest, to the bottom of the Atlantic ocean, and to the Antarctic to film such documentaries. Although IMAX documentaries have been praised for their technical quality critics have also complained that many have banal narration.

Some IMAX theaters had shown conventional films (using conventional projection equipment) as a sideline to the native-IMAX presentations. In the late 1990s there was a wave of interest in broadening the use of IMAX as an entertainment format. A few pure-entertainment IMAX short films have been created, notably T-Rex: Back to the Cretaceous, which had a successful run in 1998 and Haunted Castle, released in 2001 (both of these were IMAX 3-D films). In 1999, Disney produced Fantasia 2000, the first full-length animated feature released exclusively in the IMAX format (the film would later have a conventional-theatrical release). Disney would also release the first 2-D live-action native IMAX entertainment film, The Young Black Stallion, in late 2003.

In the fall of 2002, IMAX and Universal Studios released a new IMAX-format of the 1995 theatrical film Apollo 13. This release marked the first use of the IMAX-proprietary "DMR" (Digital Re-mastering) process that allowed conventional films to be converted into IMAX format. Other theatrically-released films, including Star Wars Episode II: Attack of the Clones, would subsequently be re-released at IMAX venues using the DMR process. In 2003 a notable IMAX re-release, again using the DMR process, was The Matrix Reloaded. Later in 2003, the sequel The Matrix Revolutions was the first feature film to be released simultaneously in IMAX and conventional theaters. Because of a technical limitation on the size of the film reel, these early DMR releases were edited to conform to a two-hour length limitation.

Reviewers have generally praised the results of the DMR blowup process, which have superior visual and auditory impact to the same films projected in 35 mm. A typical comment on Apollo 13 notes "The big effects moments, explosive sound mix, and James Horner's soaring score are all amazing in IMAX." Some large format film industry professionals claim, however, that DMR blowups are not comparable to films created directly in the 70mm 15-perf IMAX format. They note that the decline of Cinerama coincided roughly with the supersession of the original process with a simplified, reduced-cost, technically inferior version, and view DMR with alarm. IMAX originally reserved the phrase "the IMAX experience" for true 70 mm productions, but now allows its use on DMR productions as well. However, IMAX DMR versions of commercial Hollywood films are generally popular with audiences, with many people choosing to pay more than standard admission to see the IMAX version.

Noted feature film director James Cameron filmed a movie about the Titanic in 3D IMAX format, Ghosts of the Abyss.

Up to 2002, eight IMAX format films have received Academy Awards nomination with one win, the animated short, The Old Man and the Sea in 2000.

Many IMAX films have been remastered into HDTV format for the INHD channels.


Source: Wikipedia


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