Thanks Patrik
The purpose of painting the aluminum on the back of the plexiglass is to take advantage of the smooth surface instead of trying to paint a perfectly smooth surface which is not possible. Black Diamond screens have a glass front and my guess is that it is for the same reason. Also, anti glass plexiglass eliminates the shimmer. As for hot spotting, like BD, you will get some unless you position your projector on a different axis to your viewing angle. For example, a ceiling mounted projector pointing diagonally down towards the screen would work. If it was on the same level as your eyes then you would see the reflection. From the testing I have done with this, I would consider making that sacrifice because the results were so promising.
When it comes to films, 3M make a bunch that, on paper at least, sound perfect for our purposes. The problem seems to be the quantities you have to buy them in and therefore the cost. For a roll with a 60 inch width, they come in lengths of 100 feet and cost around $8000. Fine if you were starting a business but not so great for just 1 screen. Especially as need 3. ! reflective film, 1 tinted film and 1 light diffusing film. I bet the results would be good. The light diffusing film would take care of all hot spotting issues as that is what it is designed for. So that leaves us either trying to get enough people to make it worth it, or finding cheaper alternatives which I'm told are not usually in the same league as 3M products. As the old Zen Master say "we'll see". Either way, I am convinced that I want the front layer of my ultimate diy screen to be film instead of paint. The increase in image quality with a perfectly smooth surface is worth some sacrifices for me. Now that I have seen the Sony Dynaclear, I know there is no other way to go. Pro screen makers always talk about increasing contrast with "tint". I am fairly sure they mean tinted films as one of the layers in their"multi-layer" screens.
On the "privacy film", I want the micro louver effect. This is how BD and similar black screen technologies work in brighter conditions while not being massively higher in gain. They use those micro louvers to block light from certain directions and allowing it in from directly ahead (like your projector). That is one of the reasons why these screens have a narrower viewing cone than others. Some of these are also retro reflective which is another reason for the narrow cone but the cone would be narrow anyway so it doesn't matter for them. If you look at the reviews, they show a fairly steep drop in brightness (like 50%) when you get too far off center. In reality, for most people who have a large screen at home, the seating would be in front of the screen unless they have a very wide room and too much furniture. I guess those people wouldn't want any kind of retro reflective screen anyway.
On the privacy films, these work in the same way. They block light front the sides and allow light within a 60 degree cone to pass. As it is the same technology, I see no reason why it couldn't be adapted to the projector screens if you can get one that is large enough. I am getting a quote on such a film as we speak. I have asked for pricing on a custom 100 inch version. As it is a custom film, I am assuming that I will also be able to specify changes such as broadening the viewing cone if the privacy screen spec proves to be too narrow. 60 degrees though sounds similar to some of the high end screens anyway. One of the problems (in my opinion) with the commercial screen manufacturers is their desire to keep everything a secret so they can charge a lot of money for what is essentially a piece of transparent film with horizontal lines printed on it. That secret, while understandable, means they are limited to designs that preserve the secret. I was thinking that, just like privacy screens, the micro louvers film should be removable to give you options. Essentially the best of both worlds. When it is bright, you block the light from the sides and put up with a narrow cone. For the occasion when a bunch of friends come over at night and you need a wider cone, you take it off. This assumes you don't also use a retro reflective only screen. I say only because some of the glass bead screens I have been experimenting with are really bright when directly in front of them but are also still watchable from the sides if the room is dark.
On the gain of my screen, I am assuming you mean the "black screen" I pictured on this thread (I have posted a bunch on other threads too)? I don't have any special equipment to test this and I have trouble distinguishing performance in bright conditions between improvements caused by contrast vs gain. I would guess that the screen pictured is about a gain of about 1. That being said, next to a window on a sunny day, it is far more watchable that a screen I have with a gain of 2. Increasingly, I am finding that a higher gain on a white screen can make the problem worse. You have a higher gain to help with ambient light but without using some pigment to make up for the projectors lack of ability to produce a real black, you end up with a bright but still unwatchable washed out image. When I added aluminum ink (not paint) to the back, I saw an increase in gain to perhaps 1.4. I saw a similar increase when I added some aluminum ink to my black widow mix.
Based on my experiences, if given a choice between a high gain screen and a high contrast projector vs a high brightness projector and a high contrast screen, I would go with the latter if watching in bright conditions was my goal. I remember reading somewhere that after 5000:1 the human eye can't detect additional increases in contrast so when you see projectors with 30,000:1, this can only be measured with equipment and at 5000:1 it would look the same. I mention this because we are starting to see super bright professional projectors with 8000:1 contrast ratio which will do a lot more to help with light conditions. If you have a home theater projector with 1000 lumens and a 50,000:1 ratio, nothing will help with the curtains open. For me, black screens help you get a good image from a bright projector in a bright room. That said, the magazine could be wrong. Has anyone heard a different number for how much contrast the human eye can detect?
I have plenty of footage of my experiments. I will go and upload it this afternoon and post a link. I took the footage to show how bright the room was from all angles which you can't capture in a photo. I would caution that it is hard to see gain in video footage or photos as they always seem to differ from what you see in reality. They are good for comparisons though.