I'm glad to hear that this page is useful!
Bob, I like your idea of using the spray adhesive for the masking material. I even have some of that. How long did it take to set up? Did you have to hold tension on the cloth for a long time, or could you just pull it tight, hold it for a few seconds, and move on?
As for masking, there are a numbe of alternatives. The one I'm toying with right now is to build a new screen with a 'slot' in the side of the framing. The way I'm considering doing that is to have the 1 x 4's as I do now, then a some 1/4" spacers, then another 1/2" thick frame behind that, which would have the cloth attached to it.
Then, I can use the slot as a guide to slide a mask up and down inside the frame. If you want to do it manually, the simplest would be to get a couple of cheap roller blinds and mount them above and below the frame, with the ends of the blinds inside the slots. They'll be under tension from the rollers, so then all you'd need to do is affix some stops at the right masking positions, and you've have a pretty slick manual masking system. If you can't find black roller blinds, you could probably use the regular kind and either replace the cloth or dye it black. Roller blinds are almost always light blocking, so the cloth is generally something like a medium-grade canvas. They are also cheap - I just bought two of them for $15 each at Home Depot, although these ones wouldn't be wide enough (I used them for their actual intended purpose, if you can believe it!)
To attach them at the right positions on the frame for each aspect ratio you could either use a pin through the frame, or you could use rare-earth magnets harvested from an old PC hard drive, or some other fastening system.
The pin-through-the-frame idea would be simple. Since the end holder of the blinds exends through the slot in the frame, all you'd have to do is drill holes right through the frame in the front at each position, and put a metal pin through it with a little button on the end to grip it with. Pull the pin out, lift the mask past it, and push the pin back in again.
Ultimately, I'd like to motorize it, and I have some ideas on how to do that, too. By using the rollers as your tension device, you avoid the need for counterweights and springs and such. Basically, all you'd need is a motor that can be turned on and off, a few pulleys, and some cables. I plan to control it with an ADI ocelot, which is a computer controller that has X-10, IR, and solenoid-actuated outputs. I'll put some rollover switches inside the frame in the slot that get actuated as the blinds go past, and some logic in the controller that says, "If the desired aspect ratio is 2:35:1, stop the motor after the 3rd limit switch is touched. If it's 1.78:1, stop it after the second limit switch is touched. If it's 1.33:1, run it backwards until the first limit switch is touched".
That way, I can put a page on a pronto graphically showing three screens, each at a different aspect ratio. Press the right screen, and everything happens automagically.
I'm working on the theater itself right now (pictures to come soon in the Theater Construction Forum), but when that's done, I'm going to re-build the screen with the electric masking system in place.
