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How Stacking Projectors for Passive 3D CAN Work

by John Sciacca There was a blog post on our site a few weeks ago titled, “ Four Reasons to Avoid Stacking Projectors for Passive 3D Installs .” I read it. Chances are you read it too. And after reading the post I thought, “Yeah, those are all good reasons why you wouldn’t want to stack projectors. Heck, I don’t ev

by John Sciacca

There was a blog post on our site a few weeks ago titled, “Four Reasons to Avoid Stacking Projectors for Passive 3D Installs.” I read it. Chances are you read it too. And after reading the post I thought, “Yeah, those are all good reasons why you wouldn’t want to stack projectors. Heck, I don’t even really want a SINGLE 3D projector, let alone two of them!” Then, I happened to attend the Runco Training Academy at their facility in Beaverton, Oregon. (You can read about my experience here.) And there in the training room was the D-73d in all of its double-stack projector glory! Runco immediately agreed that there are definitely potential issues with double-stacking projectors, but chief architect Bob Williams commented, “We see the issues mentioned as engineering challenges to be solved.”

Runco VP of marketing, Jennifer Davis added, “I find it interesting that people believe passive 3D to be so compelling that they’ll do anything, including complicated scaffolding rigging of two projectors to attempt superior 3D. There is a reason why people are trying. Runco could have advised for years that people stack our projectors, but we share the concerns that have been raised about this kludged approach. The problem with simply stacking projectors, as these articles state, is that managing two projectors is complex and can lead to bad experiences. Issues of convergence, focus, complexity, cost, and lack of flexibility options top that list.”

It goes to reason, when you have two projectors you have two optical paths to the screen, and you need to have those optical paths in perfect alignment — or convergence — to produce a great image. And if anyone has ever performed a CRT calibration — or, dear, sweet baby Jesus, a DOUBLE-STACK CRT calibration! — then you’ll know that it can be tricky to get the best result. Williams stated, “Double-stacking projectors has been around since the beginning of projection [and] with the correct design, you have almost two identical light paths to the screen.”

Davis added, “Unlike two projectors that are installed separately, our D-73d chassis is a single projector that is easier to install than two projectors. Mechanical precision and tuned electronics allow you to converge the images.” Runco feels that its “2 in 1” chassis design makes the lenses almost perfectly aligned, and with a lens separation of only eight inches, there is much less adjustment to be made.

Once the lenses are mechanically adjusted, a lock screw is tightened so “there will be absolutely no drift of images because it is a digital device,” according to Williams. Further, Runco’s new Digital Compass allows aligning the secondary image to the primary with a plus/minus one-half pixel tolerance ANYWHERE on the screen.

The point here was that with two projectors, neither could be in the perfect position and that one would need to be so low that it might shine into the back of chairs of the head of a viewer.

Again, with a properly designed system built around two projectors from the get-go, the cabinet size and lens separation can be minimized. Davis noted, “Most two-projector set ups use an industrial mount that can add extra inches of space between the lenses, as the height of the chassis, curves of the projector, and the mount must be accommodated.”

Now, I’m not going to say that the D-73d solution is small. In fact, it would look pretty frickin’ mighty hanging from a ceiling, especially with the DOUBLE anamorphic lens kit in place. Anyone walking into your house for the first time is likely to be all, “Oh, and this must be your movie room, I see your speakers and scre… Holy CRAP!!! What is that thing hanging from the ceiling?! It’s huge!” To which point, if it is a man, he’ll probably look at you all starry eyed and want to chest bump you or shake your hand and buy you a beer and ask how in the world you talked your wife into letting you get one. And if it’s a woman she’ll shake her head in mild disbelief, likely muttering, “Boys and their toys…” under her breath and then go off and try and offer comfort and succor to your significant other. And you would definitely NOT want this bad boy to come crashing down on you; all 100 pounds of 3D might-and-fury landing on your head-brain would make 3D nausea and fatigue look like a week-long trip about the SS Pleasure Cruise. Suffice to say, mount this thing deep into wood or metal blocking. Deeeeeep. However, with the projector design, the primary lens has a 60-percent offset, meaning it can be up to 10 percent above or below the top or bottom of the screen. When you figure the height of most screens and how they are mounted, this will put the bottom of the second lens well above any interference.

This had more to do with the signal being pre-processed and split with left and right eye content going to the appropriate projectors, but I thought I would talk about install complexity here as well, primarily as it relates to the convergence issue above. So, they let me try my hand at converging the system. And I had it totally dialed-in within about 10 minutes. At another point, we changed screen sizes — from a 12-foot wide 2.35×1 screen to an 87-inch wide 16×9 screen — which required a complete cal redo. We had the system totally reworked in about 15 minutes, mechanical lens shift, focus, convergence, and all. As far as complexity goes in the install process, it is a non-issue.

As far as “no retail processors [being] available that can break down a HDMI 1.4a 3D signal to discrete left and right eye with HDCP handshakes,” well, the system seemed to work flawlessly at Runco. Sure, it requires an imposing 6U stack of processors, one to split the signal and one for each projector, but it worked. On every Blu-ray, DirecTV, and PS3 game we threw at it worked.

Commenting on this issue Davis said, “It requires third-party processing to split the signals appropriately to each projector, which introduces new brands, new incompatibilities, and new points of system failures. As many have said, there are no retail processors available that can break down an HDMI 1.4a 3D signal into discrete left and right eye with HDCP handshakes. Well, that isn’t entirely true. The 3Dimension processor, a Runco exclusive and the result of multiple man-years of development time by our top architects, software, and electronics design teams, delivers the best, most compatible 3D processing available and delivers a unique and distinct picture show to each eye.”

Yes, two projectors are going to cost twice the price of a single projector. And a V12 engine is gonna run more than a V8 or V10. Meaning that you’re gonna pay more for that new Lambo Aventador than a “cheap” Gallardo. But such is life in the world of premium luxury. Beyond the lamp costs — which can be significant on high-end models — you will need to make sure that the images are maintaining not only consistent brightness but color accuracy and grayscale uniformity between both images over the entire lifespan of the bulb AND from strike-to-strike as the projector lamps turn on. One way to eliminate this cost and worry is by eliminating the lamp completely, which is what Runco did. Their double-stack solution is a lampless design that uses LEDs that are rated to last the life of the projector with less than a 10-percent drop in light output over that span. But what about the color tracking issues? Williams said, “A built-in tri-stimulus colorimeter for each light engine takes calibration readings on each and every start up insuring accurate, calibrated color each time.”

I know that this might seem like a Team Runco PR post extolling the virtues of their technology, but that’s really not the case. The truth is, I don’t have a dog in this fight and am not really crazy on the whole 3D craze at all. (Perhaps an understatement if you consider this post…) What I can say is that I’ve spent an entire day — as in a full eight-hour day — viewing a variety of material on the D-73d, and I can say that it is the most compelling 3D image that I’ve seen and was the easiest on my eyes to view even over an extended period of time. I am definitely prone to 3D viewing fatigue and discomfort, and to my eyes Runco’s solution best addresses this issue. And while these might very well be four compelling reasons to avoid a double-stack, it seems like Runco has offered four compelling solutions. I’ll also say this, at this point in time: if I were in the market for a $70,000 projector (the price of the Runco stack with the optional anamorphic lens system) the Runco would definitely be on the short list.