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Shadowman68
04-04-2005, 10:07 PM
I was looking at my sons fish tank tonight, and started thinking about light refraction. If you put a projector behind glass, say in a custom enclosure on a ceiling or behind a wall, are there any adverse conditions that arise because of it? Light deflection, refraction, diffusion etc. Besides the obvious of having to clean the glass from time to time, are there any problems to be concerned with? What if you use plexi? I know it tends to fade or yellow in the presence of UV. How does it react to the light and heat from a PJ?
Are there really any measurable concerns?

Ghost
04-05-2005, 03:12 AM
The projector is just shooting light, so it won't be heating up the plexi; although if were talking about an enclosure with plexi front then the heat in the box could heat up the plexi, but it shouldn't get that hot in the box if your venting right/good. Still, I wouldn't use plexi - I would use glass.

If you're using good quality glass it shouldn't cause a problem. You'll only typically see a problem when there's imperfections in the glass (would recommend using the thinnest glass for the applications, the thicker the glass the greater the chance of imperfections that can cause refractions). And anything on the surface of the glass will of course cause refraction, scatter, ect... So keep it clean (same as lenes).
Also, shoot the projector at 90 degrees to the glass - meaning, straight on. Shooting at an angle will greatly increase the chance of defraction - although you can get something made for this. But then were talking lenes or special glass, not just a piece of glass (not a lot of expereince with the latter, just shot it straight I always say).

djnorm
04-05-2005, 06:13 AM
Years ago, I went to the Corning museum in upstate NY. There was a great display where they had something like 10" of standard window glass, and then a 10' chunk of optical glass. They were both polished at the ends, and the window glass was completely opaque. the optical glass was perfectly clear at 10' - you could read through it (if the letters were big enough)...

You definitely want optical quality glass...

The8thst
04-05-2005, 07:26 AM
I would talk to some of the higher end art framers and use framers glass. They will cut it to size for you, and you can get some really nice quality glass from the expensive framers.
Then just shoot straight through it.

I would also stay away from plexi. I have worked with it many many times and it scratches SO easily and is difficult to get completely clean; glass would be much better.

Caffeinated
05-12-2005, 04:18 PM
Funny i came upon this post!
Just two weeks ago I trimmed out an opening for a sony Qualia 004
we used a piece of 12 X 12" optical grade glass.

The stuff if scary clear.
It quite literally looks 100% like there is no glass there at all.

I was told by my boss - who looked into it - that you are supposed to angle the glass - so it isnt parrallel to the lens - you want the light to go through your glass at an angle. -- This prevents refraction.

Now what I really dont like about the projector behind glass thing is that you can see evry little spec of dust on the glass. (when the projectors on)

and as soon as you clean it you see the stuff flys right back on!

Any one know of a good anti-static glass cleaner???

Glackowitz
05-13-2005, 12:20 AM
I did a theater several years ago and e used a THX certified 12"12" optical glass and it was around 300-400 bills. The Projector was a Runco VX-3 in a semi-sealed box-it had a thermostat controlled exhaust system to allow ventilation. The picture was awsome, the room was pretty awsome as well...Was the Cedia best home theater level 4 in 2001

roddymcg
05-13-2005, 03:15 AM
Most movie theater projectors are behind glass, I am not sure of the specific angles and such. But it can and does work.

Anonymous
05-13-2005, 03:54 PM
There is a company called Media Decor that makes a product that competes with Vision Art. They have just come out with 1 way mirror glass that has been perfected for light transmission. Check that out.

just_program
06-10-2005, 02:44 PM
You may want to try these guys as well. http://www.opticalcoatings.com/processes/water.html

Darren
06-10-2005, 10:09 PM
I am having a "hush box" designed for a rather noisey Sanyo VPL-WF10 projector. The glass is non-reflective Edmund's Optical Glass. Pretty cool stuff, if you take a picture of if with a flash camera you get no reflection off of it.

2ndRick
06-17-2005, 09:29 PM
The reason for the angle is to keep the faint 1st side and 2nd side reflections from going back toward the lens assembly, where there would be dozens of faint 1st and 2nd surface reflections by the time you consider all of the elements.

They would again reflect back out the port and back to the lens again, and again, and again, etc. until there is a halo of "light spray" around the port and around the whole screen area.

Basically, you want an angle great enough to get the entire beam getting back into the lens, and place a light absorbing material where the light will be reflected. If it's 6 inches away from the lens, calculate the light beam size at that distance and create a sharp enough angle to clear the lens assembly.

niv
08-30-2005, 01:19 PM
Hi all,

We've done this a few times with great results, as mentioned prior you need to use optical grade water glass and angle it between 10-15 degrees. Although the glass seems expensive for such a small piece, its certainly worth it. No projector noise, that's a happy client!

best,
mark

krasmuzik
10-21-2005, 03:27 PM
Edmunds Scientific Optical glass. Any regular window framers glass or plexi - likely to be colored slightly.

http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2402&search=1