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Author Topic: Dolby 3D dual projector setups? Tristan Lane Master Film Handler Posts: 444 From: Nampa, Idaho Registered: Feb 2002 posted 01-19-2010 01:15 AM                     Julio is referring only to the light gains garnered from eliminating the dark time between alternating frames required on a traditional single projector configuration. It makes sense to me. Can anyone explain why the filters can't be placed in front of the lenses in a two projector config? Is efficiency increased by placing it in the light path prior to the engine, or is it required for functionality. It would seem much more economical to use passive filters in front of the lens.  |  IP: Logged Julio Roberto Jedi Master Film Handler Posts: 938 From: Madrid, Madrid, Spain Registered: Oct 2008 posted 01-19-2010 03:11 AM                    Different ways to look at the same thing. What I meant is that each time you put a projector into a time-sequential mode, like you do with Dolby (or RealD or Master Image, for that matter), the projector stops sending aprox. 7% of the light in "black" for the timing interval to the screen. Say this is equivalent to the light of 100Watts. If you double-up two projectors and put them both in time-sequential mode, each one would lose 7% of "potential" light output. Say this is equivalent to 200Watts. 100Watts for each projector. If instead you fit them with passive or none-time sequential filters, like we are talking here, each projector will put through the lens 7% more light. If you wanted to "compensate" for this by adding a "third projector", this projector would have to be able to output "200Watts" worth of light and perfectly halve-it to each eye without blanking. All this is aproximate as, i.e., the blanking interval for a Zscreen is closer to 10% while it can be closer to 5% for some active shutter glasses. I don't know what the mechanical Master Image is able to obtain, but I can see it's not a very good design by switching the filter horizontally instead of vertically and having such a wide gap between the filters in wheel. No idea why Dolby preferred the placement of the non-sequential filters inside the light box. I know they can be placed at the end of the light path. I suspect it is just so that they can sell "the same automated solution" to everyone. For a price. The explanation can't be that they are afraid of the luminous flux and prefer to rotate them, as the law of conservation of energy say that a filter the aprox. size of the wheel placed in front of the lens would be equivalent and able to cope with the same light, not to mention that in front of the lens is going to receive oodles of less light and heat to begin with, and probably better spreaded through the surface of the aprox. same-sized filter. If you want to check out the numbers yourself, you can go here for some measures: http://www.barco.com/projection_systems/downloads/Stereoscopic_technologies_overview.pdf There are duty cycle numbers for zscreens, active shutter glasses, time-sequential infitec (one-projector Dolby) and dual passive infitec (dual projection Dolby).  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 01-19-2010 06:33 AM                     Putting anything after the lens is not preferred. Anything in front of the lens comes off of resolution and contrast so Dolby is correct in leaving the filter between the light and the imagers. If you think about it...the only thing that is different for Dolby in a dual projector system is that the filters need not spin (and are, of course not split)...the desire to have the filters be able to be in or out of the light path remains. Steve  |  IP: Logged

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