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-   -   If we want retroreflectivity as well?? (https://www.hometheatershack.com/forums/diy-screen-development-testing/15291-if-we-want-retroreflectivity-well.html)

custard 12-25-08 08:31 AM

If we want retroreflectivity as well??
 

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Harpmaker wrote:
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custard wrote:
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mechman wrote:
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custard wrote:
i have been able to locate some glass bead paint for retroreflectivity.
it can be rollered but i suppose spraying is going to give the most uniform finish.
this type of screen should only be intended for the ones who want the brightest picture on axis i think:huh:


its 1.50am here so merry xmas and i'm gonna need to sleep now otherwise i will fall asleep while eating the turkey!:yawn:

Interesting. I was looking at something last week that I was thinking would possibly result in something like this. That stuff is pretty expensive. The stuff I was looking at would cost around $30-40 or 20-30 pounds.

Golden glass bead gel and a matte acrylic varnish. Add that to Black Widow... just thinking out loud here. :bigsmile:

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Harpmaker wrote:
I've played around with the thought of using a retro-reflective base coat, but I think such a top coat would be too much. Also, the glass beads used would have to be VERY small; the size of the bead is what makes many screens look 'grainy'. Remember the old slide projector screens of yesteryear? I have not found a source for such small beads.

My idea was to have a translucent paint over the retro-reflective base coat.

yep, the possibilities are endless with what we can try...

they do say that the beads are microscopic on the site so hopefully they are small enough.
also it is water based so it should mix in with the current mixes.

120ml of the stuff is going to cost me about $30 (£20) including postage.

i'm thinking along the lines that if we are not able to remove the bright flecks with AAA-M then it may be better to introduce it in to the AAA-F BW.
to make the AAA-F lighter we need to reduce its ratio.
a 6:1 AAA-F may get us to N8-N8.5.
whatever angular gain is lost by reducing the ratio could be replaced by the glass bead paint in a retroreflective manner.

if we can keep the amount of the glass bead paint to a minimum then cost issues are alleviated - you can buy as less as 30ml for $7 (£5).

in the end if the user wants the the best option for themselves they may be willing to pay the extra amount - it will still cost alot less than the buying a commercial paint/screen with equivalent properties.

i think i will order some of the clear (120ml) and a smaller amount of the grey (60ml) for testing purposes.

It would certainly be interesting to see how that paint worked in a screen mix. :T

My idea was that either using a retro-reflective base coat, or perhaps with the beads in the screen mix itself, the paint surrounding the beads would diffuse the retro-reflectiveness a bit to provide more gain off-axis and less on-axis. When you stop to think about it, a true retro-reflective screen wouldn't work well with PJ's since the projector is almost always mounted above or below normal viewing level.

i see your point - we dont want something that is a perfect retrereflector only. hopefully the beads are not perfectly spherical so the light is diffused out somewhat. i would have thought the projector on the table will have more to gain than a projector placed under the ceiling in this situation.

the commercial high gain screens using glass beads get around this somehow:scratch:

Harpmaker 12-25-08 10:19 AM

Re: If we want retroreflectivity as well??
 

Quote:

custard wrote: (Post 135525)
i see your point - we dont want something that is a perfect retrereflector only. hopefully the beads are not perfectly spherical so the light is diffused out somewhat. i would have thought the projector on the table will have more to gain than a projector placed under the ceiling in this situation.

My guess is that the beads would be pretty round; I think the manufacturing process lets the surface tension of the molten glass form the sphere. How they make them microscopic is a complete mystery to me. :scratchhead:

If a screen depends on retro-reflectiveness alone to create gain, then the closer the viewer is to the PJ projection axis the more gain they will see.

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the commercial high gain screens using glass beads get around this somehow:scratch:
The only way around the problem I can see is to somehow diffuse the reflected image. How to do that is the $64 question.

Many beaded screens don't diffuse at all, or extremely little; the beads can actually be removed if the screen is cleaned (they come off).

To get maximum retro-reflectiveness, the glass beads are a surface treatment only - they are only half submerged in the top coat of finish/paint/glue. To make DIY reflective signs, the beads are placed in a paper cup that has a very small hole in the bottom; the cup is shaken over the sign and the beads fall onto the still-wet paint used to make the sign. Very much like powdering a doughnut with confectioners sugar. ;)

Harpmaker 12-26-08 01:40 PM

Re: If we want retroreflectivity as well??
 

I went to Michael's Crafts today and while they didn't have the Golden Glass Bead Gel, they did have Liquitex Glass Beads Texture Gel which I assume is similar. The glass beads in the Liquitex product are way too large for anything we want to do, IMO.

custard 12-26-08 08:04 PM

Re: If we want retroreflectivity as well??
 

what would we consider the maximum size allowable?
and how large were the liquitex beads?

i take it we should be able to see them only slightly with the naked eye?

Harpmaker 12-26-08 10:22 PM

Re: If we want retroreflectivity as well??
 

Quote:

custard wrote: (Post 135870)
what would we consider the maximum size allowable?
and how large were the liquitex beads?

i take it we should be able to see them only slightly with the naked eye?

I wish I could give a size range in millimeters or microns, but I can't. I also haven't found a stated size for the Golden or Liquitex beads, but the beads in the sample chit of the actual paint could be seen as separate dots from several feet away. They were also very visible in the jar where they made contact; it looked like small pearls of tapioca.

I'm guessing that the beads themselves, in the size we want, would look like very fine sugar, or perhaps even flour.

I'm getting a new USB microscope next week (found one on sale) so I might have some photos for you.

custard 01-04-09 04:18 PM

Re: If we want retroreflectivity as well??
 

i received the samples of the retroreflective paint today.
so i did a quick test.

after shaking i dipped my finger into the mix and smeared a layer of each onto a piece of paper.

my first observation is that i can see some retroreflection aswell aswell as specular reflection. the grey mix seems more reflective than the clear mix.

i would explain the texture as similar to rubbing my finger over fine sandpaper with a grade 0f over 500.

i think the particles are smaller in the clear coat.

i will email the manufacturer to see if they can enlighten me on the actual size of the particles in the mix.

more to follow:bigsmile:

i dont wether they are that small as the the link is showing but the are definitely difficult to detect with the naked eye on the clear coat.
here are some crude pictures i took. camera is set to colour in a dark room. the photos are taken at about 45 degrees with flash on. the particles should reflect back to the camera (flash) if they are retroreflecting. quarter dollar for scale.

http://i279.photobucket.com/albums/k...0/P1010673.jpg

http://i279.photobucket.com/albums/k...0/P1010675.jpg

custard 01-05-09 02:07 PM

Re: If we want retroreflectivity as well??
 

thanks mech.

got the scope working.

heres the shots of the grey reflective paint

20x
http://i279.photobucket.com/albums/k...grtmica20x.jpg

200x
http://i279.photobucket.com/albums/k...rtmica200x.jpg

looks like there are other particles present aswell as glass beads.
the other particles are showing a prismatic coloring :thumbsdown:


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