glass bead screens - AVS Forum | Home Theater Discussions And Reviews
Forum Jump: 
 
Thread Tools
post #1 of 5 Old 06-01-2011, 11:02 AM - Thread Starter
Member
 
juan kerr's Avatar
 
Join Date: May 2011
Posts: 56
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
hi peeps,
get me new benq w6000 on friday..maybe be looking at buying a new screen..around 100 inches and electric..

been looking at this
http://cgi.ebay.co.uk/New-100-Electr...#ht_5525wt_951

anyone used a glass bead or is just white better..or maybe a grey screen?

regards juan

www.hifiwigwam.net

fantastic all new audio forum
juan kerr is offline  
Sponsored Links
Advertisement
 
post #2 of 5 Old 06-01-2011, 12:20 PM
Advanced Member
 
dovercat's Avatar
 
Join Date: Apr 2008
Posts: 839
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 193 Post(s)
Liked: 90
I answered a similar question over on AVForums so I will repost and expand my answer here. Note I own a glass bead screen, but have little hands on experience with the other types of screen.

The Benq w6000 claims 2500 Lumens but in low lamp mode, might be 20% dimmer. Lamps also vary by up to 20% and can dim by up to 20% over the first couple of hundred hours of use. (Lamp life is for half of lamps still working with at least half of rated lumens). Since it has brilliant color it might also be using a white segment or spoke time to peak white, boosting lumens and contrast at the expense of color saturation in bright colors, so lumens maybe dependent on settings. So it could be 1280 Lumens or less in reality. Still very bright.

You might want to use a camera neutral density filter ND2 with a White screen, you might need to use a ND2 or ND4 filter with a glass bead screen.

For an idea of image brightness, screen gain. A piece of white xerox photocopy paper is about 0.92 gain

(Projector Lumens / Image surface area in square feet) x screen gain = image white level in foot Lambert
Note screen gain with high gain screens like glass bead screens is very dependent on projector-screen-viewer angle, the gain spec is a max figure.

For a 16x9 screen with 1.0 gain, the required lumens are as follows
100" 87.18"x48.98" = 29.7sqft x 12fL = 356 Lumens, 14fL 416 Lumens, 16fL 475 Lumens, 23fL 683 Lumens

The target fL for a screen are:

For projection in a dark room.
The DCI digital cinema specs are 14fL reference
DCI theatrical presentations tolerance 11-17fL
The SMPTE film print specs are 16fL open gate (about 12fL for 1.85:1, 14fL for 2.35:1 due to film transparency and lenses used)
SMPTE film print theatrical presentations tolerance 12-22fL open gate (about 9-16fL for 1.85:1, 10-19fL for 2.35:1)

Some people go by the video monitor in a dimly lit room, especially if they have ambient lighting in the room. They generally opt for about 23fL.

Video monitor specs are
EBU white level 70 to at least 100cd/m2 (20-29+fL) white, older versions of the EBU spec used to use 80cd/m2 (23fL) as an example of reference white level.
SMPTE 35fL, but according to some people in practice 23fL is used.

For comparison (I would not have the projector this bright, dlp rainbows would probably make it unwatchable)
Emulating displays in living rooms with normal lighting 200cd/m2 (58fL) is used, and consumer flat panels under 50" are recommended to be capable of at least that by the EBU, for adverse conditions upto 400cd/m2 (116fL) is used.


With any roll up/down screen if you do not get a tab tensioned screen then you may end up having problems with visible waves on the screen.


Glass bead screen Advantages

It is high gain usually around 2.5, for brighter and more vivid image. (Probably way too high gain for your projector lumens - screen size)

It is retro-reflective, light bounces back the direction it came. Reducing the amount of light bouncing on to the side walls, ceiling, floor, and the amount of the light bouncing back onto the screen from the room that is being directed at the viewer. This can improve contrast.
Screen waves, in the image, if the screen is not flat, tab tensioned, are less noticeable than with a non-retro reflective screen.

Disadvantages

Limited viewing angle for best results.
Retro-reflective, reflects light back the direction it came. The more off this angle you are the less gain you get, picture brightness drops of rapidly.
Ideally you want the projector long throw, the longer the throw the less the angle projector light > screen, so the wider the viewing angles.
Ideally you want the projector lens at most 2-3 feet above eye level. Depending on the projector offset this may mean having the projector tilted resulting in the image being say slightly wider at the top than the bottom, slight geometric error is not noticeable and I would not recommend using keystoning to correct it due to the loss in image sharpness.
Ideally you want to be sitting in line with the projector-screen, so only a couple of good seats.

It maybe way too high gain, raising black level too much so image lacks depth and causing very bad DLP rainbow effect. You can increase the height of projector to decrease gain to viewers. But I think that might somewhat defeat the point of a glass bead screen, and maybe likely to cause problems with image uniformity, uneven brightness. To lower projector brightness a camera lens ND neutral gain filter could be used, then removed as the lamp dims with age.

Screen has sand paper like texture, which maybe visible in some scenes, depending on seating distance. I find it rarely noticeable and not bothersome, glass bead to me seem to have no visible screen surface when looking at images projected on to them. However some people cite screen texture as the reason they find them intolerable? Sparkles might also be visible in some scenes depending on angles and brightness.
May have very slight hot spotting, uneven image brightness, more so if people are sitting off angle. But no where near as bad as angular reflective screens. I do not find it noticeable.

Very easy to damage, can not be repaired, can not be cleaned
Fragile handle with care, if glass beads get rubbed off then you have darker patches in the image
I do not know how long it will last being repeatedly rolled up, I have mine as a fixed screen.


(Specialist angular reflective screens, instead of being retro-reflective bounce light back like a mirror or a pool table ball bouncing of the side wall, angle of incidence = angle of reflection. This makes them suitable for ceiling mounted projectors, but because the angle of incidence is greater at the far edges of the screen than at the center of the screen, they are more likely to show hot spotting, uneven brightness.)


Matt White screen

Advantages

Wide viewing angle
Screen uniformity of brightness

Disadvantages

Lower gain typically 1 to 1.2 needing more projector lumens for the same white level

Lights up the side walls, ceiling and floor more, and the light bouncing back on to the screen from the room bounces in all directions, reduces image contrast.

Depending on make of screen the screen texture maybe visible depending on viewing distance. If screen much higher than 1 gain it may have a sheen to it. If screen not perfectly flat - tab tensioned, it is likely to end up having visible waves on the image with a roll up/down screen.

Grey Screen

Advantages

Wide viewing angle and brightness uniformity

In a room with any ambient light it improves black level so perceived image depth, in comparison to a matt white screen.

It also reduces the amount unwanted room reflections washout the screen. Resulting in higher contrast in comparison to a matt white screen. As each time light hits the screen it is reduced in comparison to matt white.

Disadvantages

Lower gain 0.8 gain or less requiring a higher lumen projector for the same white level.

Lights up the side walls, ceiling and floor, and the light bouncing back on to the screen from the room bounces in all directions, reduces image contrast. But less so than matt white, see advantages.

Extremely unforgiving of any screen waves, or surface texture. Ideally you want to see it in action before you buy it.

(Specialist High Gain Grey/Black Screens attempt to combine the advantages of limited viewing angle screens like retro-reflective or angular reflective screens and the advantages of grey screens. But can suffer from the disadvantages of both.)

Projectiondesign F30 1080 VizSim with EN15 lens.130" white painted screen.
KEF Cresta 30 front speakers. Cresta 20c centre speaker. Cresta 10 rear speakers. Rega Vulcan subwoofer. Dayton Audio TT25-8 PUCK Tactile Transducers.
Samsung BD-H6500 Bluray player. Sony STR-DB930 AV Receiver (Dolby Digital/DTS 5.1)
Bat cave room.
dovercat is offline  
post #3 of 5 Old 06-01-2011, 12:29 PM - Thread Starter
Member
 
juan kerr's Avatar
 
Join Date: May 2011
Posts: 56
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
wow,
wot a reply many thanks..may i ask what screen you use?
churz juan

www.hifiwigwam.net

fantastic all new audio forum
juan kerr is offline  
Sponsored Links
Advertisement
 
post #4 of 5 Old 06-01-2011, 01:41 PM
Advanced Member
 
dovercat's Avatar
 
Join Date: Apr 2008
Posts: 839
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 193 Post(s)
Liked: 90
Very cheap Goodshin glass beaded screen 2.5 gain (measured +/-5 degrees vertical +/-7.5 degrees horizontal according to the manual, with a viewing arc of 35 degrees)
It was the 120" 4x3 tripod version sold by platinum147 on ebay UK. I removed it form its casing and have it as a fixed wall 2.35:1 screen in a bat cave all black room.

What I like about the glass bead is that to me the screen surface is mostly invisible, it lights up the side walls, ceiling, floor less and is more bright and vivid. But I would expect a 100" glass bead would be way too bright for your 2500 Lumen projector, unless you are going to use a ND filter, probably a ND4. They are very easy to damage and the screen texture is apparently an issue for some people going by posts on forums.

A more expensive glass bead screen the Da Lite High Power has its own thread. It costs around 5 to 6 times more than a cheap glass bead screen. What you get is much smaller beads and a top coat, so the surface texture is unnoticeable, and it is much hardier, I think it can even be cleaned.

Projectiondesign F30 1080 VizSim with EN15 lens.130" white painted screen.
KEF Cresta 30 front speakers. Cresta 20c centre speaker. Cresta 10 rear speakers. Rega Vulcan subwoofer. Dayton Audio TT25-8 PUCK Tactile Transducers.
Samsung BD-H6500 Bluray player. Sony STR-DB930 AV Receiver (Dolby Digital/DTS 5.1)
Bat cave room.
dovercat is offline  
post #5 of 5 Old 08-29-2012, 05:55 AM
Newbie
 
persiangulf's Avatar
 
Join Date: Apr 2010
Posts: 11
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
@dovercat
Thank you for a very good explanation of some different screen material advantages/disadvantages. smile.gif
persiangulf is offline  
Sponsored Links
Advertisement
 
Reply Screens

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off