What makes a good screen

[Luca Brazzi]

From a mechanical perspective...

Another thing to consider when it comes to screens is keystoning...

If you have a keystone issue, you can correct some/all of the keystone effect if you have a screen that you can tilt.

Im currently projecting on a white wall... but my testbed projector is straight across from the wall... when I build the final projector it may not be perfectly square with the wall so Id have some keystoning, and would rather tilt the screen up or down a bit to adjust rather than messing with the fresnels.

From an image quality perspective...

The screen needs to be matched to the projection system...

You might find this helpful:

http://www.dalite.com/education/guide.php

[Me2!]

I agree with Guy. Most gain is refering to their wallet.

Get a good white paint or a standard rollup screen.

What makes white paint white? Some are whiter than others. The difference is the quatity of pigment particles in the paint base. Cheap paint is cheap becasue its thin. White is made by titanium dioxide pigment. An example of the best whites is the Behr ultra pure white. Its at home depot. They use more pigments. The same process for making a colored paint can get you a better white. Ask the paint store guy to put 2 shots of titanium in their white.

A semi gloss has more "gain" than a eggshell finish which has more than a flat finish. As you get more "gain" you get more glare. This can make a real hotspot on your screen. Go with flat or eggshell.

I use a rollup in front of the TV. Pulling down a screen for movie time adds to the theatre feel somehow.

[Guy Grotke]

There are all sorts of experiments and commercial products that all try to improve screen brightness and contrast over something like flat white paint. This is based on the very wide dispersion of light reflected by a flat white screen. Each pixel sends light in all directions over a solid 180 degree field. If a screen material can direct all the reflected light to a narrower field, then it will be brighter.

An ideal screen would consist of one tiny mirror per pixel that would direct all the light falling on that pixel to the viewer. Anyone else in the room would see a black screen! There is actually a material that can almost do that: retroreflective glass beads. These are used on road markers, etc. to direct light back in exactly the direction it came from. So in our case, the viewer would have to have his face right beside the lens! Not so useful!

"super high gain" materials like aluminum paint reflect at such narrow angles that you see a hot spot where the angle of incidence is equal to the angle of reflection, like looking at a light bulb in a mirror. They use a curved screen to spread the hot spot over the whole image. These can be very bright, but the viewing angle is also very narrow. Good for a single-guy, not so great if you have a guest!

Some people swear by a mirror or aluminum paint surface coated with a translucent layer of white paint. The idea here is that some light leaks all the way through the white layer, gets reflected off the mirror, and then "lights up" the white layer from underneath. No science behind this, just some enthusiastic fans. One big problem with this is that it requires expert painting technique (ie. like custom auto finishing) to get it right.

My screen is painted on my wall. I filled in the texture with wallboard mud, sanded it smooth, and sealed it with white vinyl primer designed for that. Then I applied a couple of coats of Behr Ultra Pure White flat exterior, wet sanding after each coat dried. Then a couple of coats of Behr White Opalescent faux finish. Then a couple of coats of Behr Matte Clear Polyurethane. It is pretty bright with no hot spots, but not perfect. I am not that great a painter, so the reflectivity of the Opalescent layer is somewhat streaked. It is very difficult to get even, since it is transparent and the effect is cumulative as you recoat.

I actually made about 10 different screen formula test squares before I started, and then I tested it along the way, and I will confess that the sanded wallboard mud, the vinyl sealer, and the Ultra Pure White flat layers all looked very good to me. If you have enough light from your projector, I would recommend any of these. The UPW is probably the strongest surface, in terms of wear and cleaning.