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Discussion Starter #1
Greetings fellow beings
Me newbie and reading up on projection screens. Been a pleasure stumbling upon this thread and going through the knowledge shared here :T
I am so inspired by the glass beads experiment, thanks, really!!

Any updates on the beads front?

Now I'm from India and not really heard of Da-lite screens here. I do have someone from 3M coming over for a demonstration of the 3M vikuiti range of films but have no idea how they compare with the HP's mentioned here. I'm so new, the related link (between the dotted lines below) might be transparent
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so here's the google phrase to look up (1st hit that shows up) : "Vikuiti Rear Projection Film filetype:pdf"

Following are the components of the film as I understood them:
1. Film and adhesive (all of 300 microns)
a) Glass micro lenses
b) Light absorbing black PVC matrix
c) clear PVC carrier
d) removable acrylate adhesive
2. Transparent substrate - Siliconized paper? (900 microns?)

What kind of refractive index would be on those beads to let the light through from an angle of 30 degrees and not beyond?

And can the vikuiti technology be tweaked/used for front projection?

Lot's more to ask..gotta run. Waiting to stand corrected, informed :blink:
 

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Re: If we want retroreflectivity as well??

Greetings fellow beings
Me newbie and reading up on projection screens. Been a pleasure stumbling upon this thread and going through the knowledge shared here :T
I am so inspired by the glass beads experiment, thanks, really!!

Any updates on the beads front?
Hi wap! Welcome to the forum! :wave:

Nothing new on the glass beads experiment. We still can't find an inexpensive, yet reliable, source for 20 to 30 micron beads.

Now I'm from India and not really heard of Da-lite screens here. I do have someone from 3M coming over for a demonstration of the 3M vikuiti range of films but have no idea how they compare with the HP's mentioned here. I'm so new, the related link (between the dotted lines below) might be transparent.
The 3M vikuiti products seem to be rear-projection only. I don't think they would work well for front-projection.

Yes, it's missing. you need to have at least 5 posts before you can post links.

Following are the components of the film as I understood them:
1. Film and adhesive (all of 300 microns)
a) Glass micro lenses
b) Light absorbing black PVC matrix
c) clear PVC carrier
d) removable acrylate adhesive
2. Transparent substrate - Siliconized paper? (900 microns?)

What kind of refractive index would be on those beads to let the light through from an angle of 30 degrees and not beyond?

And can the vikuiti technology be tweaked/used for front projection?

Lot's more to ask..gotta run. Waiting to stand corrected, informed :blink:
The 3M vikuiti products seem to be rear-projection only. I don't think they would work well for front-projection.
 

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Discussion Starter #3
Re: If we want retroreflectivity as well??

The 3M vikuiti products seem to be rear-projection only. I don't think they would work well for front-projection.
3M did confirm it would not work for front projection, as you rightly point out. They do not have such solutions for front projection either.
My interest is really to get a good projection screen going for an ultra-short throw projector. One that comes to mind is the Sanyo DWL2500. I believe Hitachi also has one with similar capabilities. A 60" screen from 8 inches away from the screen, and 4 inches above the top of the projected image..i love!

The attached image shows the projection angles involved..albeit only in the vertical direction. It would be more extreme at the far corners of the screen.

Was wondering if a retroreflective screen would even be a suitable idea for this kind of a setup. My layman brain says we'd need a mix of specular and retroreflective qualities on the screen. :dontknow:

I've asked for some quotes from a Sovitec distributor..they seem to have a coupla products with the specs needed..now only if the price was right!! :spend:
 

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Discussion Starter #4
Re: If we want retroreflectivity as well??

Oh, and this attachment shows the setup i want..sometimes standing, and sometimes sitting, 3-5 feet away ..projecting onto glass is also on the wishlist :dumbcrazy:
 

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Re: If we want retroreflectivity as well??

Thanks for the detailed images, they help a lot!

Due to the steep angles of incidence and widely varying viewing angles in your setup anything retroreflective would be out of the question. Retroreflection means that most of the reflected light goes straight back toward the light source.

For a projection/viewing setup as you describe you would want to have as diffusive a screen as possible so you get the same image brightness no matter if one is viewing standing or sitting, on-axis or off-axis with the PJ. This means you would want a flat finish on the screen (a paint or other surface with as little gloss as possible).

This is a VERY interesting project! Please keep us up-to-date with your progress.
 

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Re: If we want retroreflectivity as well??

Thanks for the detailed images, they help a lot!

Due to the steep angles of incidence and widely varying viewing angles in your setup anything retroreflective would be out of the question. Retroreflection means that most of the reflected light goes straight back toward the light source.

For a projection/viewing setup as you describe you would want to have as diffusive a screen as possible so you get the same image brightness no matter if one is viewing standing or sitting, on-axis or off-axis with the PJ. This means you would want a flat finish on the screen (a paint or other surface with as little gloss as possible).

This is a VERY interesting project! Please keep us up-to-date with your progress.
Thanks for the encouragement :D
Was also thinking of a film which could phase shift these whacky angles to the desired range..any thoughts? Incidentally, what is the manufacturing process for glass beads? and while we're at it, how does 3M manufacture these micro level prismatic films?..like the ones here:
 

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Re: If we want retroreflectivity as well??

Thanks for the encouragement :D
Was also thinking of a film which could phase shift these whacky angles to the desired range..any thoughts?
You need to be careful with phase shifting materials since they can result in undesirable color-shifting or color-fringing of the image. If first-surface mirrors are used an image may be reflected many times in the light path to the screen, but refraction should be kept to an absolute minimum. Sometimes you have to except the lesser of two evils.

Incidentally, what is the manufacturing process for glass beads?
While I have never seen it done, my understanding is that molten glass is "dripped" through various size holes in plates and falling through the air makes the glass solidify into a sphere from surface tension. I'm sure for the smaller bead sizes needed for retroreflective screens (less than 30 micron) they have better methods.

and while we're at it, how does 3M manufacture these micro level prismatic films?..like the ones here:
My guess would be that a liquid plastic material is coated onto a metal form that has the correctly formed groves and ridges in it. After the plastic cures to a solid it is peeled from the mould and cut to whatever sizes are needed. I'm sure it's a bit more complicated than that, but that is the general idea.

Since you are dealing with such a short throw, you might give some thought to using rear-projection (just point the PJ toward the viewers). The 3M films would then work nicely. :dontknow:
 

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Re: If we want retroreflectivity as well??

You need to be careful with phase shifting materials since they can result in undesirable color-shifting or color-fringing of the image. If first-surface mirrors are used an image may be reflected many times in the light path to the screen, but refraction should be kept to an absolute minimum. Sometimes you have to except the lesser of two evils.
Interesting you mention refraction should be kept at a minimum..how do these specialized rear projection films use geometrized surfaces and glass beads and manage to avoid dispersion and fringing?

Nice insights into the manufacturing processes :T

If I have a switchable glass screen as the base surface and a one way, perforated film on top (like the one used on building facades for advertising, without any printed graphic in this case), would it serve the purpose? Sure, I'll have to take care about how well this would diffuse, but the transparency required will be achieved..
and so far as screen brilliance is concerned, I might have to sacrifice on that as the aim is to have this thing going in a stationary vehicle (like a trailer), where the primary concern becomes visibility on both sides in case of emergency situations. :gulp:

And Harp, should I take this topic off this thread/forum, since i'm only at the concept stage right now?
 

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Re: If we want retroreflectivity as well??

Interesting you mention refraction should be kept at a minimum..how do these specialized rear projection films use geometrized surfaces and glass beads and manage to avoid dispersion and fringing?
The short answer is they don't. One of the negative aspects of using a retroreflective screen is color-shifting of the image because light IS refracted both on it's way in and on it's way back out of the bead. My understanding is that the more off-axis to the PJ the viewer is the greater the chance they will notice color artifacts from this (which is quite subjective). All screens that have an optical component (beads, lenses) introduce one kind of artifacting or another caused by manipulating the path of the reflected light. There is no such thing as a free lunch. ;)

If I have a switchable glass screen as the base surface and a one way, perforated film on top (like the one used on building facades for advertising, without any printed graphic in this case), would it serve the purpose? Sure, I'll have to take care about how well this would diffuse, but the transparency required will be achieved..
and so far as screen brilliance is concerned, I might have to sacrifice on that as the aim is to have this thing going in a stationary vehicle (like a trailer), where the primary concern becomes visibility on both sides in case of emergency situations. :gulp:
Sorry wap, I'm not quite sure what you mean here. I don't know what the perforated film looks like so I can't get a mental image.

And Harp, should I take this topic off this thread/forum, since i'm only at the concept stage right now?
Mech is totally right! Discussions like this are why we have this Developer's forum! Since it's clear that retroreflection won't suite your needs we should probably break this off into it's own thread. Tell me what thread title to use and I'll be glad to do that. :T
 

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Re: If we want retroreflectivity as well??

There is no such thing as a free lunch.
there isn't ? :rubeyes:

Mech is totally right! Discussions like this are why we have this Developer's forum! Since it's clear that retroreflection won't suite your needs we should probably break this off into it's own thread. Tell me what thread title to use and I'll be glad to do that.
That would be great..Thread title could be 'Projection onto transparent surfaces' or something you feel is apt..you know my needs

I'll post about the perforated film in the new thread

Cheers :bigsmile:
 

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there isn't ? :rubeyes:
Perhaps the figure-of-speech didn't carry. What I mean is that just as there is no such thing as a free lunch (someone has to buy or gather the food items and then do the work of preparing them), there is no way to fool Mother Nature. While it's possible to design a lens system that will correct for a number of optical problems (spherical aberration and other light distortion caused by bending light rays) there is always a price to be paid for it (weight and cost of additional corrective lenses in the light path).

In the case of optically active screens (High Power, Black Diamond, SuperNova, etc.) they don't have the ability to make much correction anyway so they just put up with the negative optical aspects of the screen and only talk about the positive aspects (brighter image on-axis).


That would be great..Thread title could be 'Projection onto transparent surfaces' or something you feel is apt..you know my needs.
Done!

I'll post about the perforated film in the new thread.

Cheers :bigsmile:
:T
 

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Perhaps the figure-of-speech didn't carry
oh..it did carry pretty well..i was just kidding with the rubeyes smiley :doh:

Here is an image of a raw (unprinted) perforated film:

If you're facing the dark side, you'll be able to see through the film to the other side. Of course, the vision would not be as clear as glass permits. In commercial application, the white side is printed with a graphic for advertising (on glass surfaces such as building facades or retail windows or rear windows of cars), for example:


My idea is to have no prints on the white side. Have the white side face the PJ and images are projected onto this. Now for low trasnmittance, I plan to have a switchable lcd film behind the perforated film.
Cross section:

This Liquid crystal film will be in the off state (which makes it frosted) while our PJ is painting images on the screen. When we want to see through the window, i.e. when the PJ is not operational, the LCD film switches on to become transparent.

Perforated films are a dollar to the square meter while LCD films can be as steep as a few hundred dollars per square meter. But i'm ready to look at costs subjectively :whistling:

All thoughts welcome :paddle:

Great help starting the thread Harp, thanks again :wave:
 

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I got a demo of the Hitachi CP-250N PJ today. At 2500 lumens, 2000:1 contrast ratio, and a good crisp image onto their dull white matte finished textured interactive white board (a far cry from the DIY screen threads i've glimpsed upon HTS) with three full sized windows opened to let some decent ambient light in (albeit on a cloudy day)...and a 45" diagonal in 4:3 aspect ratio from just 12 inches away from the wall (basically how much the PJ protruded from the wall)...must admit I'm impressed :TT

Am trying to get a demo of the Sanyo DWL-2500 PJ and will buy the better of the two to kick off the experiment. I'm also ordering samples of some frosted glass films and some perforated sheets (as mentioned). Still looking for a reliable and cheap vendor for the switchable (LCD) glass film. :reading:

Please bring in your thoughts/suggestions
 

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oh..it did carry pretty well..i was just kidding with the rubeyes smiley :doh:
No worries. ;) Sometimes I forget that we are truly an international forum and certain figures-of-speech may not make it across the language barrier. Although the world does seem to be getting smaller every day.

That perforated film looks like interesting stuff! At first glance, I would be a little concerned that the hole pattern in it might generate a visible interference pattern when combined with the pixel grid of the projected image (Moire pattern), but only trying it would really determine this.

My idea is to have no prints on the white side. Have the white side face the PJ and images are projected onto this. Now for low trasnmittance, I plan to have a switchable lcd film behind the perforated film.

This Liquid crystal film will be in the off state (which makes it frosted) while our PJ is painting images on the screen. When we want to see through the window, i.e. when the PJ is not operational, the LCD film switches on to become transparent.

Perforated films are a dollar to the square meter while LCD films can be as steep as a few hundred dollars per square meter. But i'm ready to look at costs subjectively :whistling:
While I like this in theory, I think there might be a problem with the reflectance difference between the plastic film and the LCD film beneath it and that this would negatively impact the projected image. Here again only testing the theory would really tell you.

Great help starting the thread Harp, thanks again :wave:
I hope we can help provide you with info to achieve your goal. :T

I got a demo of the Hitachi CP-250N PJ today. At 2500 lumens, 2000:1 contrast ratio, and a good crisp image onto their dull white matte finished textured interactive white board (a far cry from the DIY screen threads i've glimpsed upon HTS) with three full sized windows opened to let some decent ambient light in (albeit on a cloudy day)...and a 45" diagonal in 4:3 aspect ratio from just 12 inches away from the wall (basically how much the PJ protruded from the wall)...must admit I'm impressed. :TT

Am trying to get a demo of the Sanyo DWL-2500 PJ and will buy the better of the two to kick off the experiment. I'm also ordering samples of some frosted glass films and some perforated sheets (as mentioned). Still looking for a reliable and cheap vendor for the switchable (LCD) glass film. :reading:
Assuming that Hitachi was kicking out a real 2500 lumens, that 45" 4:3 screen would have been getting hit with around 370 fL! Wow that's a lot of light. :unbelievable:

BTW, to calculate the amount of light hitting your screen simply divide the lumens of the PJ by the surface area of the screen in square feet (which can be found by multiplying the width in inches by the height in inches and dividing by 144).
 
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