# Passive 3d projection???



## rab-byte (Feb 1, 2011)

I'm starting this thread for purely academic reasons. 

First active shutter glasses give me headaches so for me passive 3D is a wonderful proposition but I have a few questions about functional implementation of a passive 3D system. 

First, what I've been able to figure out on my own. 

You need two identical projectors. Each focused evenly across you screen. The screen needs to maintain polarization. I know the SI screens Black Diamond will maintain polarization to about 30• but has hot spots at 0• 

You need to split the HDMI signal out to the two projectors and put a 3D duplexer infront of each projector, like the Optoma 3DXL, to separate left/right to each projector. 

Then you need polarizing filters placed infront of each projector. The filters need to be of the same type as the glasses you will use. 

That's what I think I know so far. Now my questions are. 

1) when viewing 2D do you simply leave one projector turned off or do you continue to play both projectors?

2) if you continue to play both won't the 2D image be too bright?

3) if you use only one then won't your lamps age at different rates? Causing issues with brightness in 3D eventually. 

4) are there more cost effective polarizing filters, couldn't I just cut a pair of glasses in half and use the lenses as filters? Or would the heat from the projector damage the plastic lenses?


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## RBTO (Jan 27, 2010)

rab-byte said:


> 1) when viewing 2D do you simply leave one projector turned off or do you continue to play both projectors?
> 
> *It's almost impossible to get both projectors perfectly registered on the screen so leaving them both on will case some blurring of the image. One is turned off.*
> 
> ...



Right now, there are only two solutions for separating the 3D HDMI signal into the left and right HDMI components needed for a passive system. Those are the Optoma 3D-XL box and the Cypress CH-322 box. You need two of each (two 3D-XLs *OR *two CH-322s, *AND* one HDMI splitter) for a passive projection system. Hopefully, someone will provide a more cost effective solution in the near future.

One related problem is that some projectors produce an output that's already polarized. This introduces a good number of complications, so it's best to choose a projector having a non-polarized output. Here's another forum that has dealt extensively with passive polarized systems.

http://www.avsforum.com/avs-vb/showthread.php?t=1280393


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## rab-byte (Feb 1, 2011)

Would use of LED projectors help with both decay of lenses and having to switch/ alternate projectors for lamp life?


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## RBTO (Jan 27, 2010)

You're still going to want to alternate projectors - even with LEDs, to even out their lifespan. In reality, it takes a significant brightness difference between projectors to be noticeable in 3D. You might have to worry about that in conventional projectors if one has a new bulb and the other is near its end, but otherwise, I don't believe brightness differences would be a big issue.

The fading is caused by the blue end of the spectrum rather than heat (most of that is removed from the output beam), and while LEDs have a narrower range of wavelengths (at each of the primary colors), the blue LED output will still cause fading. That being said, I don't think fading will be an issue for either LED or HID lamps. In summary, it would be pretty much a toss-up between conventional lamps and LED sources relative to your concerns.

I would be much more concerned about the beam polarization, if it exists, with an LED projector (this applies to some conventional lamp type projectors, also). Read the discussions in the link previously provided.


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