Using frosted plastic for rear projection

[stann]

Because our church uses a duel useage "gym-torium" during worship services, and we're in the need of a screen at the rear of the room for prompter purposes, one idea is to use a short throw projecter behind a large piece of pxyglass. Other alternatives have been discounted for various reasons. The only alternate choice would be the mounting of a 60" LCD that must be clearly visible from the distance of 53ft in a room with moderate ambient light.

Thanks for responding with your ideas, comments, questions.

[tedanderson]

The frosted glass concept is a good idea to experiment with because your R&D expenses will be minimal.

If you are a scavenger or a tinkerer of sorts, you might be able to find a discarded piece of glass from an old storm door. And if you have a projector that you can borrow, even though it might not be short throw, it will still give you a conceptual idea of what the picture could look like. Frosted glass spray paint is only about $4-$5 a can and it should be more than enough to cover the area.

[Esoteric]

I use choroplast to project on all the time. Same basic idea.

Mike

[Brad Weber]

Why not use an actual rigid or tensioned rear projection screen? I'm assuming the screen would have to be higher off the floor to maintain good sightlines and I have run into issues with using rigid plastic or acrylic screens if they are overhead, e.g. starting more than 5' or 6' above the floor, apparently there is a concern regarding their warping during the heat of a fire and falling out of the frame onto anyone below. In some cases we had to use glass screens in those applications.

Also, if the screen is higher you may want to make consider the vertical viewing angle or tilt the screen. And with a very short throw and a homemade screen, I would check to see if any resulting hot spotting is acceptable.

[dmot]

Most homemade rear projection screens have a very narrow viewing angle. That may not be a problem for you but it is something to consider. Some may even find that as an advantage. Most people in our audience who turn and look at the screen can't see anything. But if you have a wide stage you may have a problem with it.

[tedanderson]

apparently there is a concern regarding their warping during the heat of a fire and falling out of the frame onto anyone below.

Not to take this off topic but I think that in the event of a major fire, there are so many other things that can and will fall from the ceiling. I doubt that a sheet of acrylic burning and falling will be the biggest concern. I also I consider that if the fire is hot enough to burn something 6-8' in the air, chances are that it will be too hot for anyone to be standing directly underneath it.

I am assuming that the OP wants a piece of plexi vs. using a tensioned screen in case a ball hits it. Or if the screen is going to be removed and handled on a regular basis, a piece of glass or plexi is more durable than a tensioned screen.

[Brad Weber]

To be blunt, like any code compliance issue what matters is not what you think but rather what the Authority Having Jurisdiction thinks. I have had Architects that believed it was an issue and manufacturers that refused to provide acrylic screens for such applications, so it apparently is something to be considered.

I also have to disagree with your comments regarding screens that are to be transported or handled often. As a simple example, look at what rear projection screens rental companies offer or what traveling presenters use, you will probably not find a single rigid screen, they will virtually all be tensioned flexible screen surfaces. Moving and storing is also another factor to consider in many cases. It is very easy to damage the coating on rigid rear projection screens and once damaged they are quite difficult to fix properly.

Of course, in some applications the screen size also becomes a factor, just how large of a piece of solid material can you physically get into an existing space? This is probably not an issue for this particular application but I have had several rear projection screens that required being craned in prior to the roof going on or having exterior windows removed, doorways cut out, etc. in order to even get the screen into the room. I have also has projects where we had to use tensioned flexible screens because there was no way to physically get a rigid screen of the size needed into the space.

[Esoteric]

We used it because it sat on the floor (although there are no applicable codes in my area on this issue), we loved the effect, and it was 93% cheaper than buying screens. Plus the choroplast can be cut to whatever size was needed.

Mike

[tedanderson]

look at what rear projection screens rental companies offer or what traveling presenters use, you will probably not find a single rigid screen, they will virtually all be tensioned flexible screen surfaces.

I had a brain fart for a moment when I said that. I was thinking of screens that are permanently attached to the frame.

[Gracetech]

I don't know if you where thinking lexan when you said acrylic but you probably should have been. Acrylic is the lowend form of polycarbonates and is pretty much useless. As for Lexan it has the same rating as glass except for saftey and insulation which lean in favor of acrylic thickness for thickness.

The deformation temperature Lexan is in the neighborhood of 475°F. Acrylic is in the neighborhood of 180°F.

I build panels for lighting and projection out of frosted Lexan but in order for it to have a wider viewing angle the surface has to be altered. The peaking is too great with the diffusion alone but still usable for an artistic purpose(which is how i use it).

Let me know if you want some info on suppliers or tips on working with Lexan.

BTW always check with local codes because in some backwoods areas they still see all plastics as the same.

As for your use it's probably better to just go with a tension screen but that will be up to you.

crt

[Brad Weber]

Chad, I don't know if you were referring to my reference to acrylic but most projection screen manufacturers use either glass or acrylic substrates for their rigid rear projection screens and that is the basis for my comments.

FWIW, ScreenGoo has apparently developed a rear screen formula but I have no experience with it and there is very little related information on there web site.

[Gracetech]

Brad, the comment was universal in a personal manner(meaning it was for everyone). I find alot of people confuse polycarbonates so i take the opportunity to clarify, atleast on a rough level. The differences between the make ups of the polycarbonates themselves can vary with different coatings and such.

Alot of times people ask about acrylic when really they should be asking about poly substrates in general to see what material would best suit their needs. People respond thinking that the person actually meant acrylic(instead of polycarbonate) and the response comes back tailored to acrylic's strengths and weaknesses.

Just trying to enlighten the thread viewers/answer's.

crt