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Passive 3D on CRT... worth a project?

 
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[Frankie]




Joined: 16 Jun 2014
Posts: 88
Location: Italia


PostLink    Posted: Tue Oct 10, 2017 12:56 pm    Post subject: Passive 3D on CRT... worth a project? Reply with quote


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Hi! I've got in mind this project these days. I saw on the internet that there are kits to transform a projector in a 3D Passive projector by means of one (or in this case 3) Liquid Crystal Shutter that goes up to 120Hz. I guess i could make it on my own a system like that, except for the fact that i can't find any Liquid Crystal Shutter. The only one i've found was on this site: http://www.liquidcrystaltechnologies.com/products/lcdshutters.htm . This company can produce Liquid crystal shutters at the size i need to. I still haven't asked the price but i guess it will be a bit expensive.

My idea was: I place three liquid crystal shutter plates in front of the tubes with polarized filters. Then i have bought a Kit from internet, the e-dimensional 3D wired kit with a dongle VGA that goes out with a 3,5mm Jack or a 3D Vesa Plug. I connect the three shutter plates with a circuit that pilots them (that i will build if it's not that hard) with the signal that goes out the 3D Vesa Plug. Then i send a HD Resolution (720p i suppose) at 96Hz or 120Hz to the projector. the Dongle between the projector and the HTPC will exit the sync signal to the controller of the shutter plates and then it should be over. The three shutter plates turns on and off at the sync signal. So there's passive 3D on the projector, is that correct?

Let me know if you have got some ideas or corrections! Thanks for any reply!
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[Frankie]




Joined: 16 Jun 2014
Posts: 88
Location: Italia


PostLink    Posted: Tue Oct 10, 2017 12:57 pm    Post subject: Reply with quote

The projector that i think i'll use is a NEC XG 135 LC.
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AnalogRocks
Forum Moderator



Joined: 08 Mar 2006
Posts: 26690
Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Tue Oct 10, 2017 4:48 pm    Post subject: Reply with quote

With LCD shutters it would be called active 3D wouldn't it?
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kal
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Joined: 06 Mar 2006
Posts: 17844
Location: Ottawa, Canada

TV/Projector: JVC DLA-NZ7


PostLink    Posted: Tue Oct 10, 2017 5:02 pm    Post subject: Reply with quote

Correct.

Passive means you have two projectors, each with passive polarizing filters in different orientations to match passive polarizing filters that are in the glasses (one per eye). This means one eye sees one projector, and the other eye sees the other projector. There are no shutters.

Kal

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cmjohnson




Joined: 03 Apr 2006
Posts: 5180
Location: Buried under G90s


PostLink    Posted: Tue Oct 10, 2017 5:05 pm    Post subject: Reply with quote

120 Hz refresh rate at full HD requires almost 300 MHz bandwidth, well out of the range for almost any projector.

Fast P43 phosphors would be required for ghostless operation.

The LCD shutters will cause significant loss of brightness, too, as even in the "open" position they're not exactly fully transparent.
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garyfritz




Joined: 08 Apr 2006
Posts: 12021
Location: Fort Collins, CO


PostLink    Posted: Tue Oct 10, 2017 5:12 pm    Post subject: Reply with quote

The ideal IMHO would be what Kal referred to as passive -- TWO projectors. Do a stack (both projectors aligned onto the same screen) with one showing left, one showing right. Then you just need passive polarizer screens in front of each lens and in your glasses. Each eye would see the full brightness of one projector, minus the loss of the polarizer. There wouldn't be any shutter flicker and you wouldn't need the 300 MHz bandwidth that CJ mentioned. But you would have to very carefully align the two projectors. Most stacks I know of used G90's, because of their geometry control and stability. You might be able to do it with a pair of XG's, but it would be a lot simpler to stack two G90's.
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[Frankie]




Joined: 16 Jun 2014
Posts: 88
Location: Italia


PostLink    Posted: Wed Oct 11, 2017 9:31 am    Post subject: Reply with quote

I understand. I didn't want to do stacking.. but effectively i could. I have got an XG 110, a XG 135LC and a 9PG Xtra. The Xg 110 needs service and the 135LC needs at least a new green tube. I've found three new tubes of a 135LC on eBay few days ago and i see these days to buy them. Is there some guide on the internet on how to do the stacking with CRT Projectors? Later i'll search a bit anyway. And for you can it be done for example with the XG 135LC and the NEC 9PG Xtra eventually?
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garyfritz




Joined: 08 Apr 2006
Posts: 12021
Location: Fort Collins, CO


PostLink    Posted: Wed Oct 11, 2017 1:15 pm    Post subject: Reply with quote

Yes I'm sure it could, but the geometry controls on the xg and pg mean they will be harder to align than a g90.

One thing I'm not sure about is how well the polarization stays aligned when it hits the screen. I assume it must work because it's been done, but it might require circular polarizes - not sure.
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barclay66




Joined: 27 Jun 2011
Posts: 1291
Location: Germany

TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Thu Oct 12, 2017 9:47 am    Post subject: Reply with quote

Hi,

You might find this interesting:
http://www.projectorreviews.com/home-theater-and-projectors-the-technical-side/passive-3d-projection-part-1/

Regards,
barclay66
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garyfritz




Joined: 08 Apr 2006
Posts: 12021
Location: Fort Collins, CO


PostLink    Posted: Thu Oct 12, 2017 1:10 pm    Post subject: Reply with quote

Ya, that's what I suspected -- you can lose polarization when the light hits the screen, unless you use a special (and no doubt $ex$pen$ive$) screen material. Which is high reflectivity and thus has hotspotting issues.
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barclay66




Joined: 27 Jun 2011
Posts: 1291
Location: Germany

TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Thu Oct 12, 2017 4:36 pm    Post subject: Reply with quote

Hi,

There’s one exception to this rule: Dolby 3D (there’s a Wikipedia article explaining how it works)! It uses narrow-banded color filters.
Unfortunately, those filters -large enough for CRT lenses- are very expensive...

Regards,
barclay66
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AnalogRocks
Forum Moderator



Joined: 08 Mar 2006
Posts: 26690
Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Thu Oct 12, 2017 6:32 pm    Post subject: Reply with quote

Didn't Clarence have some poarizers with a batch of CRT stuff he got once?
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harry27




Joined: 04 Aug 2019
Posts: 22
Location: Los Angeles, CA, United States


PostLink    Posted: Wed Jul 28, 2021 3:35 am    Post subject: Reply with quote

I did some research on passive 3D a while ago. I found a company who apparently sells large size passive 3D polarized filters (both linear and circular polarizing), sizes up to 14" x 20" so they are more than large enough to cover CRT lenses. As long as there is no technical reason preventing CRT projectors from being used with silver polarized screen and polarized filters then it shouldn't be a problem as long as you have an external passive 3D processor and two HDMI cards.

Whether it's worth the investment/effort to get all those stars to align, well that's all up to the individual. It would be cool to see passive 3D at 72hz with CRT's good motion quality though. Also it might not be worth the potential sacrifice in image quality using a high gain polarized screen over a traditional gain screen.

https://www.apioptics.com/product-category/products/polarized-3d-filters-glasses/3d-passive-projection-filters/
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