Passive 3D Projection – Part 2
This blog is part 2 of a series on passive 3D projection. Part 1 was posted HERE. In this new blog I begin with a discussion of passive 3D projection systems for a home theater that is not specific to either of the alternative passive technologies for 3D (see my previous Blog for a discussion these alternative technologies). After this initial discussion I move on to more specifics on using polarization as the means to separate the right and left image pairs that make up the stereoscopic (i.e., 3D) image.
Passive 3D is used in the virtually all commercial cinemas for their 3D movie presentations. While active 3D projection systems (covered in several of my previous blogs) are far more popular for the consumer home theater installations, there are a few passive 3D alternatives. Some people prefer passive 3D systems, in part, because the 3D glasses are generally less bulky, lighter weight and substantially less expensive, which can be especially important if you have a large home theater that can accommodate a substantial number of viewers.
Passive polarized 3D projection systems usually involve the use of two projectors along with video processing and optical filters, either built into the projectors or provided as external add-ons. While a few companies sell such packaged passive 3D systems these tend to beyond the price range of most consumers, but suitable for commercial customers or very high end consumer home theaters. The following are two examples of such commercially available dual projector passive 3D systems. These two systems use different technologies for separating the right and left image streams for viewing. The first described projection system below uses polarization while the second system below uses the Infitec system (as described in my previous Blog – HERE).
This is a dual projector passive 3D projection system that uses linear polarization to separate the right from the left image streams. The Runco projectors use LED-based 1080p DLP light engines (rather than the more common bulb-based light engines) and are specified to produce 900 lumens in a calibrated 2D mode and 450 lumens in a calibrated 3D mode. Runco recommends a rather small screen size of 72 to 100 inches for 3D viewing. Runco refers to their 3D approach as using a proprietary “Constant Stereo Video” (CVStm) architecture. The complete system includes an external Runco “3Dimension Processor”, which uses “RealD” video processing technology, and a few pairs of 3D glasses. While Runco may use video processing that is licensed from RealD, the Runco system is not compatible with the RealD glasses widely used in commercial cinemas. With this dual projector system the right and left images that create the stereoscopic (i.e., 3D) pair are projected simultaneously, rather than sequentially as typical with all active 3D displays and with some commercial passive 3D single projector systems. The base price of Runco’s “entry level” D-73d passive 3D projection setup is $49,995 with “Optional lenses, CineWideTM, CineWideTM with AutoScopeTM, and additional 3D accessories, such as replacements glasses or premium or prescription glasses, are additional costs.”
This is a dual projector passive 3D setup using Infitec filters (rather than polarizing filter) internally fitted into each of the two C3X projectors along, which are used in conjunction with 3D glasses that use Infitec lenses. These 1080p DLP projectors use a light engine with a conventional lamp and each projector is equipped with an internal motorized mechanism that can slide the Infitec filter in the light path for 3D projection and slide it out of the light path for normal 2D viewing. Using both projectors for 2D projection is specified by SIM2 to provide a very high 7000 lumens of light output. Even with the substantial light loss when viewed (thru the 3D glasses) in 3D mode, this 3D projection setup can support relatively large screen sizes (well over 100 inches even with relatively low gain screens). The Lumis 3D package includes dual C3X projectors, a dual projector stacking bracket (for table/stand mounting), two pairs of Infitec 3D glasses and PC-based color calibration software. The list price for this the SIM2 C3X Lumis 3D system is $79,999.
Passive 3D Projection w/Polarization
For passive 3D projection based on polarization technology, the characteristics of the projection screen become much more critical than with either 2D projection systems or 3D projection systems using other technologies. As a result, when selecting such a passive 3D system, both the projector and the screen must be considered as part of the overall system. One major disadvantage of passive 3D projection systems that use polarization is the need for a projection screen that retains, to an extremely high degree, the polarization of the projected light. Such screens are typically called “silver screens” because they use a screen surface that is silver in color. A number of the major screen manufacturers offer such screen materials. For example, Stewart Filmscreen offers screens with their “Silver 3D” material which has a rated on-axis gain of 2.8 and a half-gain viewing angle of approx. 13 degrees (meaning the gain drops to 1.4 when the viewer moves to approx. 13 degrees to either side of the centerline from the screen. Da-lite offers a screen material called “Silverlite 2.5” that offers an on-axis gain of 2.5 and a half-gain viewing angle similar to that of the Stewart Silver 3D material described above. While these silver screens may have relatively high on-axis gain, the gain drops off more quickly as the viewer moves off-axis as compared to lower gain screens. Also if the projector is located relatively close to the screen (i.e., with a short screen-to-projector throw distance) there is a much greater chance of having “hot spotting” where one area of the projected image appears visibly brighter than other areas. To avoid or reduce hot spotting, longer throw distances are typically used with such passive 3D systems that use polarization (as compared to lower gain screens with wider viewing angles which are typically used for 2D projection or with other 3D projection technologies).
While one example of a commercially available dual projector passive 3D projection system is described above (i.e., the Runco D-73d) there are other less expensive alternatives.
LG offers a single projector passive 3D solution where they essentially combine the functionality of two projectors into a single cabinet with optics that allow the use of a single projection lens. The LG CF3D (Art’s full review is HERE) was introduced in 2010 and as far as I am aware, is still the only single projector passive 3D solution available for home theater use. The CF3D has a list price of $14,999 which is substantially more than most popular consumer 3D projectors using active 3D technology (such as those from Sony, JVC, Epson, Panasonic, BenQ, etc.). However the price of the LG CF3D is considerably less than the price of commercial dual projector passive 3D systems.
If you want an off-the-shelf passive 3D projection system that uses polarization, your current choices are either the LG CF3D or one of the expensive dual projector systems whose prices start near $50,000 and go upward of $200,000 for very high-end models. However, for those home theater enthusiasts that are technically inclined, there are some very interesting possibilities.
DIY – Dual Projector Polarized 3D
Do-It-Yourself (DIY) passive 3D projection systems involve using two reasonably priced consumer 2D projectors, along with commercially available external processors and optical (e.g., polarizing) filters (plus a few other odds and ends). You will also need to buy or fabricate the mounting hardware for the stacked pair of projectors and in many cases also fabricate the mounting for the filters. The 3D glasses with suitable polarizing lenses are generally available. Finally you will need a “silver screen” for compatibility with this type of passive 3D projection. The follow illustration attempts to depict the basic functional components that make up such a DIY system.
I expect it to require several blogs to properly cover each hardware element and overall system considerations of such a DIY passive 3D system, so I will be writing about this for some time to come.
Next time will be Part 3 on passive 3D projection which will continue the discussion of Do-It-Yourself dual projector passive 3D projection systems.