Originally Posted by Lee Stewart
So the brouhaha is about Sony projectors. Well what about Christie and Barco who have many more digital projectors in cinemas than Sony does. They are both single lens 3D projectors.
Sorry this is quite long, but I wanted to try and be complete.
In general, most of the DLP installations are doing frame alternating 3D where the projector switches between showing the left eye and then the right eye, typically at triple frame rate. So the projector is showing 144 frames per second, 3 left and 3 right, times the 24 frames per second. There are 4 different systems in use presenting this triple flash 3D to the audience. Real-D which uses either a "Z-screen" or the "XL system". Dolby 3D which uses alternate RGB color filtering, Master Image which uses a spinning disk of alternating polarizing segments. and Xpand using shutter glasses. All 4 systems have some advantages and dissadvantages. Real D with a single Z-screen was the first system put into wide use. It is not very light efficient and suffers from a bit of image softness and ghosting/crosstalk. If used with a bright enough projector and carefuly setup, it does provide a very good image with only a minor loss in sharpness and color saturation due to projecting the image through the LCD polarizing Z-screen. Real-D XL is an improvement in many ways, but also adds some new problems. It's biggest improvement is in light output. Well over 40% more light gets to the screen comared to a single Z-screen system, but the light out of the projector is split into 2 paths and have to be recombined back at the screen. I have seen it line up perfectly with ease, but I also spent a solid hour tweaking one and was unable to get the image split to less then 4 pixels at al the edges. I think the box had been dropped and the prisms were mis aligned on that one. The XL box does have 2 images coming out of it, stacked vertically at the projection port, but they are both showing both eyes at full resolution. According to Real-D, 2D should NOT be projected through the box or Z-screen. When the projector is operating in a 3D mode, it is sending a sync signal to drive the LCD active polarizers. When running a 2D feature, this signal is not there and the panels do not behave correctly and could even be damaged. 2D contant such as trailers are often shown before a 3D feature in 3D mode and this is not a problemas it just shows the same image to both eyes. A full 2D feature could be shown in 3D mode this way, but is not done in any of the theatres I have been in. Unfortunately, the real-D screen or box on the front of DLP projectors is not normally motorized to move out of the way, so it does sometimes get forgotten and a few shows run through it. The effect on the picture is not horrible, but can be visible. A little dimmer and softer, and you may see the pulsing of the non synced LCD's. The XL boxes do fall back to a fairly fast mode so it will not damage the LCD's and the flicker is usually fast enough to not be visible. At least two other companies are making motor kits to push the box out of the way when not in a 3D mode, but theatre owners tend to be cheap. Master Image is very similar to Real D in that it is using alternate circular polarizing but instead of using an LCD polarizer it mechanically changes the filters by spinning them in front of the projector on a large motor. It uses 12 segments so the amount of tilt is fairly small. The light efficiency is right between the original Z-screen and the XL system from Real-D. Both systems can use the same glasses and require the silver screen to hold the polarization. Master Image does have one very nice feature, it comes with a motor system to move the spinning disk in and out of the projectors light path to switch in and out of 3D without human help. Dolby 3D is a bit different. Since it is using the shifted colors it works on white screens. The light efficiency is a bit less since it does not have the help of the high gain silver screen, but it also does not suffer the hot spotting and color shifts caused by the silver either. The color filtering is done in the projector before the DLP chips so the image from the chips to the screen is not going through anything extra. The left end right eyes are using different primary colors so the calibration is more involved and care has to be taken to get it right, but when done correctly, the colors are very accurate and vivid without the loss of sharpness and contrast suffered by going through the polarizers or other extra glass. The lower light in the center of the screen is easilly made up for with the much more even light right out to the corners. In many cases people think it is brighter overall when using the same projector and lamp size since shadow detail at the bottom and sides of the screen are lit better. All Dolby 3D systems using a single projector will use only one lens and the filter wheel is powered to move out of the light path during 2D operation. Xpand also works on white screens and has the more even light advantage. The glasses are LCD shutters so they suffer similar light loss to Dolby 3D or a single Real-D Z-Screen. There is nothing in the light path from the projector to the screen, the only thing effecting the image is the glasses on your face. Some people swear by the active glasses, other swear at them. They are heavier and need battteries. They are expensive and fragile compared to the passive glasses. Dolby glasses are also more expensive than the polarized ones and are therefore reused and washed like the Xpand ones, but are far more durable and don't need batteries.
Some larger screen theatres have gone to dual projectors. Digital IMAX is also a dual projector system. Real-D and Dolby can do dual projectors in 2 ways. The best is to dedicate one machine to each eye like IMAX does using static polarizers or fixed color shift filters in each machine. When running in 2D, it is common to then use only one machine, alternating on a show by show or day by day basis to keep the lamps at the same life. IMAX still overlays the two images and claims it increases resolution, but even if perfectly aligned, I see that as a tough act to prove. The DLP pixels do not leave much gap at all to fill with the other projectors pixel, but it does blend away the pixel edges a bit.
Xpand using 2 machines still has to have the machines in sync alternating eyes to match the glasses, so there is less advantage to 2 machines, you only get more light, nothing else. Being able to dedicate a machine to each eye eliminates the lag between the eyes where one eye is seeing the new frame first. This can cause a blurring of shuddering look in fast motion and even a loss of 3D depth on horizontal motion.
The SONY 4K projectors are using SXRD, Sony's own version of LCOS imagers. They are not able to alternate between the 2 eye images at 144 hz like the DLP's can. So they had to do 3D in a different way. After quite a bit of testing they came up with the dual lens system causing all the uproar in the Boston Globe. Basically, they went back to the way 3D was done on film in the 80's. They split the imager in half vertically. One half is always showing the right eye, the other half is always showing the left eye. This does give both eyes the new frame at the same time so it does work very well in moderate motion. The problem is that the 3D lens is a beast. It needs to be installed and aligned very carefully to get the two images perfectly overlayed. The 3D lens also does not have any provision for automated adjustments. So the images need to be scaled and fit to the screen depending on the format between flat and scope. Much of the imager ends up blanked and off the screen. This results in a lower resolution, and light output compared to using the full imager for 2D. Since the Boston Globe article came out, several theatres have started changing the lenses for bigger features. Maximum light output is cut to less than 1/2 when the 3D lens is installed versus the 2D only lens. Several theatres have also pulled fairly new SONY projectors out of larger screens as they just could not put out enough light. The DLP projectors not only hold a larger bulb, they put out more of the light the bulb creates. SONY claims 18,000 lumens out of the model 220 projector with a 4,000 watt bulb, the 320 may be a bit better, but I don't have the spec. The typical DLP with a 6,000 watt bulb is over 30,000 lumens. Barco is using a new 6,500 watt bulb and putting out close to 40,000 lumens.
TI is starting to ship 4K DLP projectors. Currently the DCI spec for cinema does not include a 4K 3D format, but one is going to come. For now, all 3D is only 2K resolution. IMAX does label their shows as 4K 3D, but using two 2K DLP projectors is not going to make a 4K image. True 4K projectors like the Sony and new 4K DLP's have 4 times te pixels, double in both directions.
If I did not answer a question you have, please post it or PM me and I will try to clarify anything I may have missed.