Appreciate your extra info -
Was that fine weave or coarse weave canvas? (slightly irregular)
Did you use a base or primer coat prior to the luminous white paint?
Was the paint in matte or satin finish? In this thread Guy Kuo states that it must be the matte finish - would you concur? http://www.avsforum.com/ubb/Forum9/HTML/000017.html
Can you still see the weave of the canvas through those 3 coats of paints?
Is there much light going through your screen onto the wall behind it?
Does the center of your screen noticeably reflect more light than the edges?
How does it compare with each sample from Stewart and Draper?
Yup! I guess half the work in making a home-made screen is posting about it here!
Thanks again for sharing your insights with us.
My screen will also be wider than 8' (sheet of sheetrock). Here's a link to Vern's home theater with screenshots of his large 1.0 gain painted sheetrock screen (5' x 12'): http://members.home.net/tvdias/
However, I am considering using fiberboard, which I believe it is available in larger sizes than 4' x 8'. However, it must be rigidly framed and suspended from my uneven wall as the fiberboard is light but flexible.
Then maybe an oil-based coating in a can (called in France "enduit gras") which is used for smoothing plaster or sheetrock walls prior to painting them with high-gloss lacquers (not planning to use glossy for a screen).
The issue is whether it would be preferable to keep the texture of the fiberboard, or to have a flat & smooth surface.
Afterwards possibly a coating of titanium primer to increase reflectivity.
The issue here is whether this would increase hotspotting as well.
Then, depending on what primer is used and how much I want to balance its reflectivity with that of the surface paint, one or more coats of white paint - yet to be determined.
There was a lead from Alan Gouger for screen paints - did anyone follow up on this? http://www.avsforum.com/ubb/Forum9/HTML/000022.html
A friend suggested an idea to choose among paints:
Hold up a flashlight (do full spectrum flashlight bulbs exist?) to the top of the paint cans and find the one that reflects the most light WITHOUT REFLECTING THE IMAGE OF THE LAMP!
This technique should hold true for other surfaces - fabric, synthetics or paper.
His contention is that we need a screen surface that reflects light while scattering it somewhat rather than just directly bouncing it off.
Maybe for this reason it would also be better to retain some texture to the screen surface rather than make it totally smooth?
You are quite right that the cheapest way to go, if you plan on making a painted screen, would be to use as a support the wall that you already have. However, is it totally flat?
This could be an issue for converging and focusing your projector. (In Europe, older walls are seldom flat, and often the newer ones aren't that much better, with poorly aligned sheetrock). The coating you apply will also be a critical base treatment, if only to cover the tape around the edges. You may want to check out Raoul's second post in this thread: http://www.avsforum.com/ubb/Forum2/HTML/002213.html
You are quite right to question the role of the surface texture in light reflection. In art (paintings) there is a noticeable difference between the luminosity of those painted on canvas, on wood, on ivory or on copper. And that is with alot of texture from the paint itself. But even if you think that some sort of weave is preferable, you could always apply a layer of the synthetic fabric that is used to prevent cracks in plaster cielings, a thin synthetic woven veil that could lend a "screen texture" provided that you use a very thin layer of paint over it.
Let us know if you try a coat of silver first, though I think titanium is considered to be the most reflective? Some issues with silver are here: http://www.avsforum.com/ubb/Forum9/HTML/000215.html
As for the FP versus RP debate: The exerience of viewing a image with the light coming at you is quite different from that of light reflected off a surface. The latter is similar to the movie theater, as it follows the same principle, whereas the former is more like a direct view TV. FP in ambiant light also depends on the technology you use.
For daylight viewing without light control (blinds, heavy curtains...) you'll be forced to either go with a high brightness front projection such as LCD/DLP/D-ILA or if you choose a CRT projector (for deeper blacks, truer colors...) then you would have to go with a curved screen (14 gain!) but it could hurt with respect to picture distortion and viewing angle.
For that last option, see post by Alan Gouger, of AV Science fame, How to build a curved screen: http://www.avsforum.com/ubb/Forum9/HTML/000040.html
You're definitely on to something!
This is exactly the type of product that the commercial screenmakers can't realistically put on the market because of its fragility for shipping and handling, and the extra care the customers would need to exercise in its use.
But for our purposes, it may well yield picture performance that even the best brand-name screens in the world couldn't match? Who knows...maybe Faroudja will demo with our finds at the next CES? <g> In any case, it just goes to prove that in pooling our ideas, the dynamics of combined ingenuity just can't be beat.
Would you know if Sentinel or Milano can provide samples for testing?
Hope we can get to the bottom of this.