The IMAX system has its roots in EXPO ’67 in Montreal, Canada where multi-screen films were the hit of the fair. A small group of Canadian filmmakers/entrepreneurs who had made some of those popular films, decided to design a new system using a single, powerful projector, rather than the cumbersome multiple projectors used at that time. The result: the IMAX motion picture projection system, which would revolutionize giant-screen cinema.
The intent of IMAX is to dramatically increase the resolution of the image by using a much larger film frame. To achieve this, 65 mm film stock is run horizontally through the cameras. While traditional 65 mm film has an image area that is 48.5 × 22.1 mm (1.91 × 0.87 in) (for Todd-AO), in IMAX the image is 69.6 × 48.5 mm (2.74 × 1.91 in) 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.
To create the illusion of three-dimensional depth, the IMAX 3D process uses two camera lenses to represent the left and right eyes. The two lenses are separated by an interocular distance of 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 then projecting them simultaneously, viewers experience seeing a 3D image on a 2D screen. The IMAX 3D camera is cumbersome, weighing over 113 kg (250 lb). This makes it difficult to film on-location documentaries.
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 linearly polarized as they are projected onto the IMAX screen. By wearing special eyeglasses with lenses polarized in their respective directions to match the projection, each eye can only see the image intended for that eye since the lens’s polarization will cancel out the other eye’s image.
The other method for 3D projection involves the use of LCD shutter glasses. The projectors display each frame of film alternately for each eye (while one projector’s image is displayed, the other is blocked), at an effective rate of 48 frames per second. The glasses contain LCD panels that alternately block the light in one eye while allowing the other to see th
e image. The shutters flash back and forth in sync with the projector, such that each eye only sees the image intended for it.
IMAX HD (48 fps)