Film-Tech Forum ARCHIVE: 3D on a white screen?

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Posted by Justin Hamaker (Member # 2165) on 06-18-2015, 10:51 PM:

I know RealD has a white screen 3D system, but this is not what I'm asking about.

Using a MasterImage Clarity3D system on an NEC2000C with a 3K bulb, is it possible to do 3D on a normal white screen (I don't know the specific specs of the screen).

The auditorium where I would try this has a relatively short throw (40 feet), and if plenty bright for 2D with the bulb at about 65-70%. Currently we only run 3D in our larger auditoriums with a 4K bulb cranked up to about 90-95%. As the popularity of 3D declines, I would like to be able to use a smaller auditorium for 3D, but I don't know if I can convince the company to spring for another silver screen.

If this is not possible, I'm curious to know what is the difference between the white and silver screen which affects 3D.

Posted by Stephan Shelley (Member # 8587) on 06-18-2015, 11:01 PM:

Systems like Master Image and Real D use polarization for the filtering. Unfortunately a normal white screen scatters the polarization and you loose the filtering. A silver screen retains it. Real D's new low gain 3D screen also retains the polarization. Dolby 3D uses a spectral filtering and works on any screen.

Posted by Dave Macaulay (Member # 813) on 06-19-2015, 12:40 AM:

With a matte white screen your choices are:
1)Dolby® 3D with an expensive motorized filter wheel in the projector and expensive enough glasses that you won't want them stolen plus a glasses washing unit and staff to work it. I think adding the filter wheel to an NEC NC2000 is not too bad, it's quite a trick on some projectors.
2) A liquid crystal glasses system like XPandD that adds a transmitter unit for the signal and expensive enough glasses that you won't want them stolen plus a glasses washing unit and staff to work it. And - the glasses have batteries to change or keep charged.
Both are inefficient, I think Dolby® 3D sucks out more light but have never done an A/B test for that. You may think you have lots of light... but don't count on it.
I would recommend Dolby® 3D. The glasses, although not cheap, are passive filters: no electronics or battery to fail. They are also lighter and less cumbersome. I have seen XPanD in quite a few studio and FX company screening rooms where they will not tolerate silver screens... but these places are small and don't deal with "the public". With Dolby® 3D you can install a beeper gate system to remind people they "forgot to return" the glasses (I think they come with a transponder built in), and the washing unit is pretty simple.

Posted by Steve Guttag (Member # 268) on 06-19-2015, 06:28 AM:

Dolby 3D with xenon is about 8-10% efficient (depends on how much color correction needed for each eye...make sure you set your projector configuration files properly to minimize having to over correct).

XpanD is closer to 18% efficient but you are talking about glasses that are upwards of 5x as much as Dolby's.

Dave's comments above are accurate.

Remember though with non-RealD systems, you don't have a "partner" collection 50¢ for each ticket so your potential profit is significantly higher.

However, since you have RealD...check your contract. They normally demand an exclusivity with their deal. I've only heard of grandfathering in other systems if they were in place before signing the RealD contract.

Without a doubt, the white screen systems look better than the silver screen ones. For reasons I won't go into here a lower gain screen running with a lower center brightness will appear brighter, overall, than a higher gain screen running at a higher brightness. That is, if you set up a silver screen (gain typically 2.2 - 2.5) for say 4.5fL in the center and set up a 1.5 gain white screen for 3.5fL in the center, the white screen system will appear significantly brighter.

Posted by Manny Knowles (Member # 1171) on 06-19-2015, 11:55 AM:

And I hate seeing 2D on a silvered screen.
Hot spots.

Posted by Mark Gulbrandsen (Member # 72) on 06-19-2015, 02:06 PM:

quote: Steve Guttag
I've only heard of grandfathering in other systems if they were in place before signing the RealD contract.

They wldn't even allow us to to that at a couple locations so I had to gather up all the Master Image units and put them all at one site. Eventually that site was sold off and the M.I units went with them. I HATE HATE HATE their rotating disk units! All they are is crud suckers. FYI: Real-D told me a couple years back that they WILL sell their units too.

With the current 10K up front deal they want now for a leased unit its a wonder they are even still around. I don't know a soul that has installed any recently.

Mark

Posted by Carsten Kurz (Member # 5396) on 06-19-2015, 02:18 PM:

quote:
know RealD has a white screen 3D system,

This is NOT a white screen 3D system, but a 'silver screen that appears white'.
It's still a polarizing 3D, just with an improved screen surface that looks more like conventional white screens (less gain, less hotspot, etc.). You can not use a polarizing 3D system on any 'real' white screens.
Other manufacturers have developed similar screens. I haven't seen a comparison yet, but e.g. Harkness 'Clarus XC' is also an improved silver screen technology.

http://www.harkness-screens.com/clarusxc/

- Carsten

Posted by Marco Giustini (Member # 4544) on 06-19-2015, 03:04 PM:

quote: Steve Guttag
Dolby 3D with xenon is about 8-10% efficient

My tests have never gone more than 7.5%!

And Manny, I hate Silver Screens, period! [Smile]

Posted by Mark Gulbrandsen (Member # 72) on 06-19-2015, 04:31 PM:

MDI was the forst with the high gain white surface. They wanted something like 25 USD a square foot for the stuff when it was first released... I bet today and with the other competition that they can't even give that stuff away...

Mark

Posted by Justin Hamaker (Member # 2165) on 06-19-2015, 04:52 PM:

So if I'm understanding this correctly, a standard white screen does something to the polarization of MasterImage and RealD. It's not just an issue of reflected light.

Posted by Dave Macaulay (Member # 813) on 06-19-2015, 05:40 PM:

Polarization is preserved after polarized light reflects off a mirror like surface: the silver 3D screen is that kind of reflective. A matte screen is not: polarization of incident light is almost all lost on reflection. So no polarized system works, you just see both eye images through both lenses of the glasses.

Posted by Lindsay Morris (Member # 1430) on 06-20-2015, 04:22 AM:

I use Dolby 3D on a 10M screen outdoors with the NEC1600 & a 4Kw lamp @ 90% power & get reasonable 3D images...certainly nice sharp focus right across the screen & very even light.
Did a bit of research by checking out the other local hardtop sites doing 3D & theirs appeared brighter square onto the screen but as to be expected with a silver screen considerable drop off on the edges. Plus much softer focus. Also to me the 3D depth...if you can call it that was far better than what I saw in RealD sessions I checked out.

The machine came with the 3D unit fitted (a S/H low hours NEC) so thought I would try it with the few glasses that also were supplied BEFORE going to a bigger lamp than the 2.5Kw one initially fitted.
Was certainly well underlit with that lamp size but VG 3D effect & nice even focus so dived in for a bigger lamp & more glasses.
The glasses we clean manually. 2 big tubs of water one hot-ish with detergent & the other warm to rinse & then let them dry off in the sun with a final check & wipe over with isopropyl alcohol before stashing them away.
150 pairs take about a bit over an hour to process & most likely we will continue doing that as only occasional 3D sessions so no big deal cleaning them like that.
Might well be different when we have a full house of 300 for a 3D session.
Lindsay