Front or rear projection, perhaps both, on ultra short throw system? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 15 Old 08-02-11, 08:37 AM Thread Starter
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Front or rear projection, perhaps both, on ultra short throw system?

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
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 filetypedf"

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
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post #2 of 15 Old 08-02-11, 11:33 PM
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Re: If we want retroreflectivity as well??

Quote:
wapeye wrote: View Post
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
I am so inspired by the glass beads experiment, thanks, really!!

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

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

Quote:
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.

Quote:
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
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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post #3 of 15 Old 08-03-11, 06:38 AM Thread Starter
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Re: If we want retroreflectivity as well??

Quote:
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.

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!!
Attached Thumbnails
Front or rear projection, perhaps both, on ultra short throw system?-dwl2500-throw-distance.jpg  

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post #4 of 15 Old 08-03-11, 06:50 AM Thread Starter
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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
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post #5 of 15 Old 08-03-11, 02:42 PM
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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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post #6 of 15 Old 08-04-11, 04:53 AM Thread Starter
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Re: If we want retroreflectivity as well??

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Harpmaker wrote: View Post
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
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:
Attached Thumbnails
Front or rear projection, perhaps both, on ultra short throw system?-3m-prismatic.jpg  

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post #7 of 15 Old 08-04-11, 07:59 AM
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Re: If we want retroreflectivity as well??

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wapeye wrote: View Post
Thanks for the encouragement
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.

Quote:
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.

Quote:
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.
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post #8 of 15 Old 08-06-11, 07:10 AM Thread Starter
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Re: If we want retroreflectivity as well??

Quote:
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

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.

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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post #9 of 15 Old 08-06-11, 07:14 AM Thread Starter
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Re: If we want retroreflectivity as well??

by 'these films', i mean:
Attached Thumbnails
Front or rear projection, perhaps both, on ultra short throw system?-3m-prismatic.jpg  

Front or rear projection, perhaps both, on ultra short throw system?-3m-rear-proj.jpg  

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post #10 of 15 Old 08-07-11, 08:45 PM
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Re: If we want retroreflectivity as well??

Quote:
wapeye wrote: View Post
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.

Quote:
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.
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.

Quote:
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.
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