The Renaissance of 3D:
How the New 3D Technologies Work
Another implementation of 3D in commercial theaters uses a technology called interference filters, made by the German company Infitec. This system uses one projector and does not require a silver screen. Infitec 3D compatible projectors have a special color wheel inserted between the lamp and the imaging device itself that divides the primary colors into discrete sections. Think of it this way: where there once were red, green, and blue, there are now red-1, red-2, green-1, green-2, blue-1, and blue-2. Special interference filter glasses allow the left eye to see only the "1" sections while the right eye sees only the "2" sections. The glasses use additional filters to correct color perception so what your eyes see is as close as possible to the original film. You may have seen this technology already: it is known as Dolby 3D in commercial cinemas.
Dolby 3D is not nearly as widespread in cinema projection as polarized 3D systems are, but the world premiere of Avatar at the Empire Cinema in Leicester Square, London, was shown in Dolby 3D.
Advantages of Interference Filter 3D
Passive glasses. Passive glasses are a common element in 3D systems designed for commercial theaters and other large venues both for their ease of use and for their relatively low cost. Interference filter 3D glasses are more difficult to produce than are polarized glasses. As such, they are built to last. The lenses are made of glass and the heavy-duty plastic frames even have a slot for an anti-theft device. They are more resistant to scratches and scuffs than the more flimsy polarized lenses.
No silver screen. Several decades ago, silver screens were used for all movies, but they fell out of favor. Silver screens have more restrictive viewing angles than do white screens, so when projectors became bright enough to light up a white screen sufficiently, silver screens fell by the wayside.
What was true about silver screens then is still true now: brightness falls off significantly for viewers sitting off-center. In a commercial theater this can include a significant portion of the audience. Since interference filter 3D does not use polarization it does not need a silver screen, thereby improving the viewing experience for everyone in the audience. People along the sides of a theater get more consistent screen illumination while everyone in the audience gets color fidelity on par with non-stereoscopic film.
Disadvantages of Interference Filter 3D
Light loss. Any single-projector 3D display method suffers from significant light loss compared to 2D display on the same projector. This does not mean that single-projector interference filter and polarizer systems are always the same brightness, or that dual-projector implementations are always brighter than single-projector systems. Single-projector polarized systems, interference filter systems, and shutter glasses systems all share this limitation.
Specialized equipment. It is possible to install a single-projector polarized system like RealD on an existing DLP Cinema projector, which many commercial cinemas already use, without actually altering the projector itself. Since the Infitec 3D mechanism works inside the projector, theaters need to either purchase cinema projectors pre-fitted with the Infitec color wheel or have the wheel installed inside their existing DLP cinema projectors by a trained engineer.
Expensive glasses. The major advantage of passive glasses is that they are inexpensive, so one might expect Infitec 3D glasses to be inexpensive as well. They are not. Most of the manufacturing cost of Infitec glasses is in the lenses themselves - the glass must be given several coatings to help them differentiate between the wavelengths used. The most recent Dolby press release related to 3D glasses has their wholesale price at $27.50 per pair. Obviously this represents a significant expense to a participating theater, so great lengths are taken to ensure the glasses are safely returned by theater patrons. One Dolby 3D theater I attended required that I hand over a picture ID in exchange for the glasses.
|Contents:||What is 3D||Anaglyph||Polarizers||Interference Filter|