Glass sand-blasting beads in DIY screen - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 29 Old 09-13-12, 07:30 AM
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Re: Glass sand-blasting beads in DIY screen

Hi Guys,

I'm a long time lurker, first time poster from The Netherlands and let me say just what a great work everyone here does. The amount of information is just astounding.

These glass beads are intriguing, especially now that they seem to be available in the right sizes for a reasonable price. I've been looking into building my own polarization preserving screen for passive 3D viewing, but so far I've not started yet because of the constantly reported problems with hot-spotting. I'm wondering if these beads could be used on top of an aluminum based paint to create a retro-reflective polarization retaining screen. Basically that should eliminate the perceived hot-spot in the center of the screen by turning the entire screen into one giant hot-spot. What do you guys think, would this have any chance of working?
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post #12 of 29 Old 09-13-12, 09:02 AM
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Re: Glass sand-blasting beads in DIY screen

Quote:
Chrodarcniss wrote: View Post
Hi Guys,

I'm a long time lurker, first time poster from The Netherlands and let me say just what a great work everyone here does. The amount of information is just astounding.

These glass beads are intriguing, especially now that they seem to be available in the right sizes for a reasonable price. I've been looking into building my own polarization preserving screen for passive 3D viewing, but so far I've not started yet because of the constantly reported problems with hot-spotting. I'm wondering if these beads could be used on top of an aluminum based paint to create a retro-reflective polarization retaining screen. Basically that should eliminate the perceived hot-spot in the center of the screen by turning the entire screen into one giant hot-spot. What do you guys think, would this have any chance of working?
Hi, welcome to HTS!

I don't know for sure, but I think all the refraction of the light rays as they pass through the glass beads twice (once going in, reflecting off the backing and then coming back out) would depolarize the light rays.

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post #13 of 29 Old 09-13-12, 10:05 AM
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Re: Glass sand-blasting beads in DIY screen

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Harpmaker wrote: View Post
Hi, welcome to HTS!

I don't know for sure, but I think all the refraction of the light rays as they pass through the glass beads twice (once going in, reflecting off the backing and then coming back out) would depolarize the light rays.
Thanks, good to be here

Yeah i am/was afraid of that. I guess I can do some testing to see if going through a lens depolarizes the light, but it makes sense. Too bad
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post #14 of 29 Old 08-01-13, 07:10 PM
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Re: Glass sand-blasting beads in DIY screen

My diy glass bead experiment. Seems to work if done right and is fairly cheap.

While it looks like I just got a shipment in from Columbia, it is in fact powder sized glass beads.
Attached Thumbnails
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Glass sand-blasting beads in DIY screen-5.jpg  

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post #15 of 29 Old 08-02-13, 07:31 AM
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Re: Glass sand-blasting beads in DIY screen

Wow pretty interesting results. It's a bit hard to judge from these pictures, but it certainly seems to reject ambient light very well. Does it increase the gain as well?

What method did you use? Did you pray them on or just spread them over wet paint and shook of the excess?

Can't wait to see some more results!
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post #16 of 29 Old 08-02-13, 06:51 PM
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Re: Glass sand-blasting beads in DIY screen

I did neither. I couldn't get good results by dropping it on top of the paint. Mixing the glass with the paint doesn't work at all. They loose all reflective properties if they are completely covered in paint so you need at least some of the glass exposed.

I found that sprinkling it on wet paint meant that it either sunk in too far or not enough of it stuck so I ended up with a shimmer on top of whatever screen surface was underneath.

In the pic, I had an undercoat which is aluminum ink (not paint) mixed with a little black paint which gave me a slightly tinted metallic surface. With a brush, I then painted a really thin layer of carbon fiber resin. This is basically a transparent epoxy. With a brush, I was able to coat the surface with a layer that was thin enough to leave most of the glass exposed. This kind of epoxy is sticky enough to glue an elephant to the ceiling. No joke, I really suggest gloves for this unless you are ok with a sand paper like consistency on your hands which may be uncomfortable in certain situations!

Before the exposure dried, I just tipped the bag of glass over the surface and tilted it until it covered every bit of exposed epoxy. It takes less then you might think. Only a thin layer of glass will stick and the rest will fall to the next but. When it is all covered, the remainder will just fall off when tilted and can be reused. Within 45 minutes, it will be rock solid. The next day, any excess can be brushed off and it's ready for testing.

On the increase in gain, it kinda depends where you are sitting. You need to be opposite the screen and ideally, on the same level at the projector. I was using it more as a translucent light diffusing layer to give me a watchable screen on a surface that would normally have been too dark. With the lights on, it gave me a really clear high contrast screen with amazing depth. With the lights off, it is noticeably a little brighter than the white screen. I saw a larger increase in gain when I applied the glass to a plan white surface which I also found to be a waste of time. In bright conditions, it isn't gain that suffered with white screens, it's contrast and even with greater brightness, blacks still look washed out.

One thing I would say about glass powder sized beads is that you do end up with a really smooth, but well diffused surface. Nothing like the visible sand like texture I have seen with larger beads.

I am always skeptical about the gain numbers claimed by commercial screen makers. They often claim a gain of 2.5 for their glass bead screens but the ones I have seen are all white and still look terrible with the lights on when using a dim home theater projector. Has anyone ever seen a white glass bead screen that looked good in a well lot room?

Either way, this method is cheap enough to warrant a few experiments if you are like me and enjoy that kind of thing.
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post #17 of 29 Old 08-02-13, 06:57 PM
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Re: Glass sand-blasting beads in DIY screen

I know the pics aren't great. I had to reduce the quality to upload them. You can see the white screen looking washed out as the lights are on and the room is lit from 3 directions. The high contrast glass bead screen looks far more watchable which reflects reality. I can tell you that it takes a lot of light to make this projector look washed out on any surface as it is 5000 lumens which may give you some idea of what the screens are dealing with. I had to shine a sun lamp in the direction of the screens to challenge them.

I have a number of projectors ranging from 700 lumens to 8000 lumens. My quest is more for good blacks with the lights on rather than just more gain to supplement an under powdered projector. What kind of projector do you have?
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post #18 of 29 Old 08-02-13, 09:16 PM
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Re: Glass sand-blasting beads in DIY screen

Very interesting! Can you give us a source and stock number for the beads you used?

As for posting higher resolution photos, you might think about using Photobucket or other free image hosting service and then posting a link or thumbnail that will allow the full res. photo to be seen.
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post #19 of 29 Old 08-03-13, 05:47 AM
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Re: Glass sand-blasting beads in DIY screen

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Daylightuser wrote: View Post
I have a number of projectors ranging from 700 lumens to 8000 lumens. My quest is more for good blacks with the lights on rather than just more gain to supplement an under powdered projector. What kind of projector do you have?
I see. Actually I build DIY projectors for special applications, people that want it hidden in a closet, project through the ceiling, that kind of thing, so I'm not new to experimenting. These kind of projectors used to be very lumen challenged, but these days, with great advances in LED technology, sub-optimal lighting conditions and bad black levels are fast becoming my biggest problems, so this kind of application is extremely interesting for me.

That you are basically bouncing this of a metallic tinted black surface and still end up with a slight gain increase is pretty amazing. That explains the extreme difference in contrast between the beaded screen and the white screen. I could see this working well on quite a few other surfaces depending on conditions. In my home I have a projector projecting through the wall right above my head and a large window in the left wall. The lighting conditions aren't as bad as what you described, but my projector doesn't have your lumen output either. I've been wanting to try a black widow screen for some time, but I was always worried that the gain loss would hurt too much. This seems like a great solution to remedy that .

Keep up the great work!
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post #20 of 29 Old 08-03-13, 05:50 PM
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Re: Glass sand-blasting beads in DIY screen

I like to understand the effectiveness of as many diy methods as possible, even if I don't end up using them. Here are some pics from my ambient light test for the purpose of selecting a screen for my set-up. For the purpose of the test, I have an overhead light on with 3 100 watt bulbs and the blinds are open during a sunny afternoon. That is about as bright as I would ever try and watch a movie in for real world use.

I will post again to explain what they all are in a minute.
Attached Thumbnails
Glass sand-blasting beads in DIY screen-set-0-conditions.jpg  

Glass sand-blasting beads in DIY screen-set-1.jpg  

Glass sand-blasting beads in DIY screen-set-2.jpg  

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