Christie is one of the largest providers of DLP-based digital-cinema projectors, and it always has a big booth at NAB. This year, the company demonstrated a new laser-illuminated projection system designed to display Dolby 3D. Unlike RealD and Imax 3D, which use polarized light to isolate the left and right images, Dolby 3D uses slightly different wavelengths of red, green, and blue for the left and right images—hence the term "6-primary"—and the glasses allow only the appropriate wavelengths to reach each eye.
One big advantage of Dolby 3D is that it does not require a silver, high-gain, polarization-preserving screen—a low-gain white screen can be used for both 3D and 2D content. Silver screens suffer from hot spots, narrow half-gain angles (the viewing angle at which the apparent gain drops by half), and more speckling from laser light. Plus, theaters with silver screens for polarized 3D must use the same screen for 2D presentations, which is hardly ideal.
The Christie system uses two 4K projection heads and lasers tuned so the wavelengths of red, green, and blue are each separated by about 20 nanometers. Each head can produce 60,000 lumens of light output (twice the output of xenon lamps), resulting in a peak brightness of 14 foot-lamberts reaching each eye, which is phenomenal for commercial 3D—typically, you get 2-4 fL per eye, leading to the common complaint that 3D is very dim. Also, Christie claims a contrast ratio of 1000:1, which is 10 times better than the typical stereo contrast ratio. And of course, the lasers last tens of thousands of hours, while xenon lamps must be replaced every thousand hours or less at a cost of thousands of dollars a pop.
The two projection heads were oriented facing each other with a vertical offset, and 45-degree mirrors reflected the images to the screen.
Using two projector heads means that the left and right images are both shown simultaneously rather than sequentially as in RealD theaters, which represent over 90 percent of all 3D theaters. (Imax 3D uses two projectors, so its left and right images are simultaneous as well, while many Dolby 3D theaters use only one projector and a filter wheel to present the left and right images sequentially.) Many experts agree that sequential images are less desirable because they are more apt to cause discomfort such as eye fatigue than simultaneous images.
The demo consisted of clips from Avatar, Frozen, and The Hobbit: The Desolation of Smaug. All were 2K source files upscaled to 4K, and The Hobbit was shown at 48 fps (the others were at 24 fps). The Da-Lite screen was 17' wide with a gain of 1.0.
This was the best Dolby 3D I've seen to date—the image was nice and bright with great colors, deep blacks, and nary a hint of crosstalk. Also, internal reflections from the back of the lenses in the glasses were less noticeable than I've seen before, though I still saw a milky halo in the periphery of my vision. When I asked a Christie rep about it, he said, "They're working to improve that." I sincerely hope so—internal reflections and haloing are my main criticisms of Dolby 3D, which otherwise has a lot going for it.
Editor, AVS Forum
I've seen a few setups online using dual projectors for passive, polarized 3D, but having it rotated at 90 degrees then angled down looks interesting too. Probably makes it easier to dial in geometry convergence between the two images, with the anamorphic lenses (clearly visible in the picture) in the light path.
This is inspiring me to consider a cheap-o solution by buying another BenQ w1070 projector and using this kind of setup. Although it could be perhaps done easier with two projectors sandwitched and just use the vertical lens shift to align them.
Isn't there a new projector screen tech coming out with much better 3D performance than a silver screen? (for passive 3D). I read it on AVS somewhere. That would be killer to get in my apartment. 3D needs all the lumens it can get. I even wonder if one can alternate frames between left and right projectors to achieve 120hz in 2D as well. Although I'm not really familiar with how long each image is held so it's probably not going to work.