IMAX is a motion picture film format and a set of proprietary cinema projection standards created by the Canadian IMAX Corporation. IMAX has the capacity to record and display images of far greater size and resolution than conventional film systems. Feature films have traditionally been upconverted into IMAX format for display in IMAX theatres, though some have been partially shot in IMAX.
A comparison between 35 mm and 15/70 mm negative areas
IMAX is the most widely used system for special-venue film presentations. As of September 2010, there were more than 445 IMAX theatres in 47 countries.
IMAX uses "ESTAR" (Kodak's trade name for PET film) base. The reason is for precision more than strength. Developing chemicals do not change the size or shape of ESTAR, and IMAX's pin registration (especially the cam mechanism) does not tolerate either sprocket – hole or film – thickness variations. The IMAX format is generically called "15/70" film, the name referring to the 15 sprocket holes per frame.
The film's bulk requires platters rather than conventional film reels. IMAX platters range from 1.2 to 1.83 metres (3.9 to 6.0 ft) diameter to accommodate 1 to 2.75 h of film. Platters with a 2.5 hour feature film weigh 250 kilograms (551 lb).
The 15 kW Xenon short-arc lamp used in IMAX projectors, the GT 3D projector (dual rotor) used two!
GT 3D projector (dual rotor) Water cooled reflector for the left eye projection
GT 3D projector (dual rotor) Water cooled mirror for the left eye projection
GT 3D projector (dual rotor) Water cooled mirror for the right eye projection
Drawing the large film through the projector presented challenges for both the camera and the projector. Conventional 70 mm systems were not steady enough for the 586× magnification. On the projector side, William Shaw 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 "aperture block". The projector uses a vacuum to pull the film into contact with this lens. This the "field flattener" flattens the image field. The lens is twice the height of the film and connects 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 xenon short-arc lamps are made of a thin layer of fused quartz and contain xenon gas at a pressure of about 25 atmospheres (367 PSI); because of this, projectionists are required to wear protective body armor when changing or handling these in case the lamp breaks (e.g., due to a drop to the floor) because of the danger from flying quartz shards when propelled by the high pressure of the Xenon gas within.
An IMAX projector weighs up to 1.8 t (2.0 short tons) and at over 178 cm (70 in) tall and 195 cm (77 in) long.
IMAX Corporation has released four projector types that use its 15-perforation, 70 mm film format: GT (Grand Theatre), GT 3D (dual rotor), SR (Small Rotor) and MPX, which was designed for retrofitted theatres. In July 2008, the company introduced a digital projection system, which it has not given a distinct name or brand, designed for multiplex theatres with screens no wider than 21.3 m (70 ft). All IMAX projectors, except the standard GT system, can project 3D images.
In this report I have attempted to describe how the best possible - but also most expensive - analogue 3D presentation could be achieved in cinemas using 70mm film and how it is still used today with IMAX.
Most newer IMAX films are now using the IMAX digital sound DDP designed by Sonics. DDP is short for Digital Disc Playback. The system is a digital sound source specifically made for IMAX. Sonics uses compact disc technology to create the highest quality sound delivery possible today. Wide frequency response, dynamic range and the accurate perception of time are the attributes of DDP. A frequency response of 20 – 20.000 Hz is maintained over the entire audio spectrum of ten octaves. Six octaves is found in conventional cinemas.
Behind the screen
Imax theatres require a sound system able to produce believable effects and operate reliably at unusually high power levels. The Imax sound system by Sonics provides extremely high sound quality that does full justice to the unique film presentation. A Sonics sound system operates in an environment which is quite different acoustically from most other theatres. The Imax film program depends on the optimum performance of the combined projector and sound system to achieve maximum audience impact.
In 1988, Imax acquired Sonics Associates Inc. as an affiliate. Alabama based Sonics is a world leader in sound system design and offers customers the benefits of more than 26 years of research and hands-on experience in the IMAX theatre network.
I have listened to the system many times with hi-fi enthusiasts, and they always say it is the best cinema system they have heard. Because of the enormous power you can always hear all details.