People with the ISCO anamorphic lens on DLP and DILA projectors have noted that there is a bow top and bottom and pincushion on the sides. Poster "Kam Fung" has suggested this might be corrected with a curved screen. Since a parabolic (curved on both horizontal and vertical directions) screen doesn't seem practical when the screen cannot be fixed-mount, I'm thinking of at least trying to make a horizontally curved screen.
My goal with a curved screen would be to get the absolute best focus across the entire screen. I can also see how a curved screen would reflect more light back to a 60 degree viewing cone than a flat screen. If I could achieve those two things, it would be worth doing.
I do have a problem, however. Any screen I put up, flat or curved will need to hang in front of a big bay window. So the DIY screen Alan built would not work for me. While I could theoretically make a screen with frame and fabric as Dean considered doing, which would be light enough to hang and remove, it doesn't seem very practical. (Although, I've also considered whimsically of a screen like this that was reversible and could hang on a side wall with movie poster or other art on the flip side. Ironically, with the concave side of a curved screen to the wall when displaying artwork, it would be much less susceptible to smudging or other damage !)
However, if I were to try to build a roll-up curved screen, here is what I'm thinking:
The screen fabrics from Draper that have a textile backing -- namely the F1500 -- say they hang flat without tensioning. Here's what I was considering doing for a curved screen:
1) Take a 9' length of 1"x8" wood or plastic.
2) Draw an arc of 25 feet radius as in Alan's DIY screen.
3) Use a router to carve a T slot along the curve. Mount this to the ceiling.
4) Make a screen from the Draper fabric with backing material.
5) On top of screen have flexible plastic edging to fit in the track.
6) On bottom edging of screen have sewn in 2" tall 1/2" wide strips of lead that are 1/8" thick.
7) To one side of the screen location, put a home-built roller and casing for the screen. Or possibly buy a roller & case assembly for a 60" pull-down screen and throw away the original fabic.
To use this screen, you would draw it from the roller sideways across and through the track. The lead weights would provide vertical tension, but there would be nothing to hold the curve across the bottom of the screen.Now for my questions to those of you experience screen users.
Does this sound reasonable ? I figure the total weight along the bottom edge would be more than ten pounds, and segmented into half-inch weights. Would this be enough to pull the screen taut and maintain the curvature dictated by the top track all the way to the bottom ? Or would a solid curved piece for the bottom, affixed after the screen was unrolled be better/easier. How heavy is the dowel normally on an 8 foot wide screen ?
Is the F1500 fabric stiffer in one direction than the other ? Is it intended to "rollup" in only one direction ? If so, I may have trouble getting a 60" x 110" piece of fabric with the right orientation.
Of course, this is all moot if the ISCO lens really provides a planar focus and not parabolic. http://www.avsforum.com/ubb/frown.gif
That's why I am so interested in exactly where the best focus is at the sides of the screen. Across an 8 foot width, is it flat to the screen, 2" in front of it, 3", "4", "etc.
This has turned out to be longer than I expected. Thanks for reading -- if you got this far ! http://www.avsforum.com/ubb/biggrin.gif