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-   -   Cieling mounted DLP - What gain screen ?? (http://www.avsforum.com/forum/23-screens/19047-cieling-mounted-dlp-what-gain-screen.html)

Phat Phreddy 07-08-2000 06:46 AM

I have now assembled most of the parts of my HT and the last item I really need to work with is the screen.... I am currently using some blackout curtain fabric with a Viewsonic DLP. As the light output is modest (575 lumens) and I have some ambient light creeping through curtains in daytime I am considering high(er) gain.... I have the problem of a fairly 'wide' room and viewing area so must consider this.

What works well with these type of projectors ??
When a screen has a 'viewing angle' is this the complete 'cone' it can be viewed in or the angle away from 90 degrees (projected light) that refection occurs at ??? ie is a 30 degree cone just 30 degrees or 30 degrees either side ??
When using a roll down 4:3 screen does rolling it down only halfway to give widescreen aspect ratio's create problems for the screen fabric or wrinkling ??? and does this method work for tab tensioned screens ???

Ideally I would like a electric tab tensioned screen with variable stop positions to give me a 4:3 185:1 and 2.35:1 for all eventualities... is this too much to hope for without some drawback like wrinkling etc ???



BrewsterMan 07-11-2000 08:26 AM


I will try to answer some of your questions.

First, it sounds like you are needing a screen that has a modest gain while still providing you with a fairly wide viewing angle. Having said that you will probably want to look at a screen surface with a gain of about 1.3-1.5. This will give you a little boost but not too much as to accentuate a hotspot and reduce your viewing angle by a great deal.

Speaking of viewing angles, most of the screen manufacturers measure gain in what they call "half-angle" or "viewing angle" the terms are used synomously. What it means is at what angle from the center do you have half of the brightness you started with. Therefore, if a 1.3 gain screen is stated to have a 45 degree viewing angle. At 45 degrees from the center it has a gain of .65 . Hence you would have a viewing "cone" of 90 degrees since you have to include both sides of the screen center.

As for bringing a manual 4:3 screen part way down, you should not experience any wrinkling by doing that.

To answer your last question, yes indeed there are electric screens that will do what you are asking. I believe that Da-Lite and Stewart are the only two that make electric "roll-up" screens that will mask out the top and bottom of your screen. Based on what I have seen, I personally like Da-Lite's version. The reason it is preferred is because their masking is done automatically. The Stewart has to be done manually through relay timing. Da-Lite has a cool system that is preset and goes to the correct aspect based on which one you choose. Speaking of which, it does four different aspect ratios (4:3, 16:9, 1.85:1 and 2.35:1). The control for this screen is a wall switch that is low voltage and can be interfaced very easily with your favorite controller. If you need to know more about it, check out their web site at www.da-lite.com . The screen you are looking for is called the HORIZON.

Hope this helps,

Phat Phreddy 07-15-2000 09:01 PM

The horizon is well out of what I intend on spending for my current needs..

Also the aspect ratio change provided by the horizon was not what I had meant. I mean to have a 4:3 roll down screen and only use 2/3 of it for a centered 16x9 panel, or work out how to use xyx and my HTPC to raise the 'used' pixels to the top of the DLP panel and use even less of the screen out in the open (I prefer my movies high on the wall anyway http://www.avsforum.com/ubb/smile.gif )

I see no real reason why I cant do this and surely this is the best 'all aspect' screen variable full screen, widescreen and scope without excess to be masked... The only problem is if the screen wrinkles as it is partly deployed...

Thanks for your explanation of viewing angle but a very 'newbie' question on the following statement "Therefore, if a 1.3 gain screen is stated to have a 45 degree viewing angle. At 45 degrees from the center it has a gain of .65" that clears up my question about viewing angle beingh half the light cone or the full light cone but I am guessing that when you use the 'gain' numbers to be 1.3 or .65 this is in relation to a flat white mat surface being 1.0 ??? 1 gain from any angle ??


BrewsterMan 07-18-2000 05:59 AM

Yes you are correct. The basis for gain measurements is a substance known as Magnesium Carbonate (MgCO3). This is also what is used to make Matte White screens. Magnesium Carbonate is considered to be a perfect diffuser and disperses light in all directions equally. This is the starting point when you are talking about gain.

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