History and IMAX 3D technology

How we see
The fact that our left eye and right eye see objects from different angles is the basis of 3D photography. If you try looking at an object through one eye and then the other, you will notice that it slightly changes position. However, with both eyes open, the two images that each eye observes separately are fused together as one by our brain. It is the fusion of these two images that creates normal binocular sight and allows our brain to understand depth and distance.

Pre-cinema
To replicate this process on film, two camera lenses are used in place of our two eyes. In 1838, Charles Wheatstone invented the world's first stereoscopic viewer based on Renaissance theories of perspective. Constructed of an assortment of angled mirrors, his invention contained two separate drawings - one for the left eye and one for the right. When both images were observed at the same time, Wheatstone's viewing device produced a stereo image. Weatstone's device encouraged the beginning of a new era in motion and still photography.

3D Cinema
Filmmakers place the two lenses of a 3D camera at about the same distance apart as the distance between our eyes. This space is referred to as the interocular distance, or interaxial distance, and is typically set at about 2-1/2 inches.

To project a 3D film, two individual images representing the perspective of the left and right eye are simultaneously projected on screen. Without special glasses during the presentation, it will seem like you are seeing double, because in fact you are seeing double. Fortunately, the 3D glasses correct this problem. Each lens of the 3D glasses has a special filter which blocks out the opposing image, allowing each eye to see only one image. Your brain perceives the fusion of the two separate images as one three-dimensional image.

Projecting 3D Film
There are several ways to project the dual images necessary to exhibit a 3D film; however, not all processes require two separate projectors. The anaglyphic film format simultaneously projects two different, offset images from one single strip of film. One image is coated with a green (or blue) colour, the other image is coated red. Spectators are given glasses that sort one green (or blue) lens and one red lens. The green lens of the glasses cancels out the red image on screen, while the red lens of the glasses cancel out the green (or blue) image on the screen. Your brain processes the two separated images as one 3D 'black and white' image!

To see 3D in colour, the images for the left and right eye must be kept separate. Before the advent of today's large format theaters, which use two separate synchronized projectors, previous methods placed two 35mm frames in various configurations, either over and under each other or side by side.

Modern Improvements
Contemporary 3D films have begun to use computer generated imagery (CGI) to maximize the 3D illusion. Use of computer created images allows filmmakers total control over convergence and focus, the two most problematic aspects of live action 3D production. By creating the environment in the computer, the point of convergence can be precisely set by the filmmaker. Furthermore, the entire frame can be kept in focus, something nearly impossible to do when shooting by conventional means. What this means is that when the film is projected onto the screen, you will absorb the visual information much like you would in the real world, thus maximizing the illusion.