Alternative rear screen materials and other questions - AVS Forum
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post #1 of 2 Old 01-07-2000, 03:42 PM - Thread Starter
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I'm trying to avoid spending a fortune ($10K for a standard Fresnel/lenticular between 84" and 90" wide, 16:9). Besides the SLP:
http://www.thescreenworks.com/New_Pr..._products.html

at about $2K, I came across this:
http://www.jenmarvs.com/products/index.html

This is Jenmar visual systems; they make those big video walls. Video processors break the image into segments which are displayed on individual RPTV modules, each containing an 800x600 DLP projector.

They're right here in Silicon Valley, so I went and took a look.

They had a 64" wide RP setup using a Plus 1100 running the reptilian HD loop. It looked great. The screen was completely unaffected by ambient light, perhaps with even better perceived contrast than with the lights off due to the pupils closing, along with its highly nonreflective properties (0.4% diffuse reflectance, 0.2% specular reflectance).

The specs say the transmission is 60%, but I'm skeptical based on the samples I got. Supposedly a 2X difference isn't that different in perceived brightness; subjectively I'd say the transmission is 20% based on looking at the shadows cast with various light sources. The fellow at Jenmar says 2000 lumens would be needed to properly illuminate an 84" wide screen, which sounds way too high. Gain is 1.7.

Peter, have you seen this stuff?

The Jenmar gobbles up too much light, and the SLP is available only up to 76" width.

Since these screens are unstructured, I wonder if it's feasible to get, say, three 60" (36" x 48") 4:3 screens, bond them along their long edges with optical cement, making a 108" X 48" screen, and then trimming it to 85" X 48".

What do you think, Peter?

questions on rear screens:

1) The expensive component is the Fresnel lens. If a unity gain diffusion screen is used, why is one necessary? My readings say a diffusion screen takes light at any incoming angle and disperses it in a hemispherical pattern. If this is true, then even the extreme rays from a short-throw lens should be dispersed the same as the collimated rays from a Fresnel.

2) Presumably real screens don't diffuse ideally; is there a rule of thumb (or quantifiable amount of hotspotting) that says at what throw ratio a Fresnel is not needed?

3) Mirrors are also very pricey, jumping astronomically in price at the size I need, at least from Dalite. Peter, do you have any more reasonably priced sources?

4) Which type of DNP screen was used in that installation on your web site? Are you a DNP (or other brand) dealer?

Thanks

Noah

[This message has been edited by noah katz (edited January 07, 2000).]

[This message has been edited by noah katz (edited January 07, 2000).]

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post #2 of 2 Old 01-10-2000, 05:23 PM - Thread Starter
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Peter,

Thanks for responding.

Yes, it's the Blackscreen material. It would cost about $3K, which I thought was less than than a Fresnel that size would cost - is that right?

By dark glare filter, do you mean material not specifically intended for a RP screen? Does it contain a diffusing medium?

$2K - music to my ears! Is the Stewart simply a tinted diffusion screen? I presume that mild hotspotting refers to this screen; what throw ratio projector are you assuming? The shorter the throw ratio, the more hotspotting (assuming no Fresnel), right? If I add a second smaller mirror, I can go up to a 1.8:1 throw ratio, and the projector ends up in a much more convenient place, too.

What do you think of Draper Cinescreen Cine 25 with Cine 13HC high contrast tint and Armor Kote coating? About $2.4K.

"My of the cuff recommendation is the one above..." Which one - Fresnel/glare filter or the Stewart?

Thanks!

Noah

[This message has been edited by noah katz (edited January 10, 2000).]

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