Homemade Mounting of retractable curved screen ? - AVS Forum
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post #1 of 7 Old 06-26-2000, 12:56 AM - Thread Starter
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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

Kirk

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post #2 of 7 Old 06-26-2000, 04:39 PM
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The bottom curvature is exressed with the use of a plastic bar of some sort that has some give. It is attached to the bottom edge of the screen. It is secured with matte black non stretching twine of some sort.... for the exact duplicate of the top curvature. Done. Exactly like mis-stringing a recurve bow.

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post #3 of 7 Old 06-26-2000, 04:46 PM
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Actually, the top could be expressed the same way as well. when done, the tension could be released, and the screen rolled up. Because of the curvature, it would be unlikely to suffer from inconsistencies of the useable surface. Anchor it to the floor with bungee, and forget the bow thingie. one bungee in the middle, and one on each end. hmmm... on second thought, that would only bring constant inaccuarcy. Stick with the double- pressure releasable bow, and use the bungee floor anchors to keep it stretched tight.

There you go, one easy to make and maintain, portable, removable, curved screen. It's too bad it won't assist in multiple planes...

[This message has been edited by KBK (edited June 30, 2000).]

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post #4 of 7 Old 06-26-2000, 06:53 PM - Thread Starter
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A simple cord to hold the bow with flexible plastic edging, eh ? Well, that is certainly simple. What will keep the whole affair from wracking from left to right, though ? I figured weight and gravity would stand a better chance of keeping vertical plumb.

And I'd have to get up out of my chair to hook the cords on top and bottom ! The curved runner on top at least holds out some hope for motorized extension and retraction via remote control, provided nothing is necessary across the bottom. If the bottom didn't need to hang in free space, then a track there would be the obvious most stable and accurate method.

PS. I read your painted screen posts. How is that working out ? Has Andy gotten any results from his beta testing back to you yet ?

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post #5 of 7 Old 07-02-2000, 07:24 AM
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Which magnets are those? The ones I keep strapped to my head?

Just pondering again, or expanding on my thoughts that occurred as I wrote the earilier message.

A manufacturer could create a curved tensioning motorized screen where as the tensioning system locks itself in place it could also lock in the top and bottom curvature.

The top curvature would release itself from an inset in the roller at the end of the screen extraction. The motorized sysyem would 'finish' with the pulling of steel cord for the curvature.

Cord for pulling it tight is not even nessesary. wire could be used inside of a oversized piece of flexable material, metal or plastic. Sort of a two piece-sliding construction, if you can catch my meaning.
OR, two piece, bu the second piece hinged to the other along it's entire length. Pulling a wire at one end, like an accordion-like umbrella tensioned system.


Hmmm. better yet...Let me properly explain. The backing piece of plastic (the one closest to the wall) has small bits of U-shaped pieces of plastic attached to it where the legs of the U shape are rivet-hinge attached to the top and bottom of this horizontally placed screen bottom plastic piece. The bottoms of the U shape are smaller (skinnier than) the upper parts by a hair. This change in thickness is graduated in it's change as you go from top to bottom.
If you placed a bunch of them together by themselves, they would describe an arc, like a bunch of orange slices placed together.
Put a hole on the inside of the bottom of the 'U' shape and run a steel cord through them. Anchor the cord at the one end, and pull the cord tight at the other end, thus forcing the pieces into a exact repeatable arc. You can even eliminate the backing piece of plastic and hinge the pieces together for a simpler system. This tensioning would be the last bit of motion in the motorized tensioning sytem, and the first to be undone at roll-up.

Exact replication of the curve due to small changes in tension and wear in the system would have to be looked at. The cord system would be the most reliable and repeatable in it's performance.

Although it is possible to use this system to create a curved fabric screen in both the horizontal and vertical dimensions, for portable and permanent deployment, there are several factors which lie in the way of such advancement. In the horizontal plane, the problems lie only in the singular plane. In the addition of a vertical component, the entire curvature of the screen surface enters the picture and creates another quandary. Have fun with that one. Now that this thing is stuck in my skull it won't leave until an answer is found. Gee, thanks for the brain itch... Just pile it on top of the rest.


[This message has been edited by KBK (edited July 02, 2000).]

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post #6 of 7 Old 07-02-2000, 09:26 PM - Thread Starter
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Very interesting, KBK !

I considered thin strips running the whole height of the screen as a backing, and having each slat form a part of the arc required, but it hadn't occurred to me that they could actually be tensioned to hold the curve. The slats would need to be trapezoidal on the cross-section and strung together along the inner (small end of trapezoid), right ?

It would take some thought to figure out how to get the tension applied by the motorized extension mechanism. I'll keep an eye out to see if you post a scratch for this itch.

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post #7 of 7 Old 07-03-2000, 09:17 PM
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The slats are an interesting idea, and will be considered for future use. In the case of a singluar curve described along the horizontal axis, the slats would cause slight changes in the surface in the vertical domain(the changes would happen across the horizontal, but be oriented in the vertical). The best bet is to tension the system from top to bottom, and use an array of the 'oranges' to describe the arc, one row on the top and one row along the bottom. using a extended spring arrangement that locks at each end (in conjunction with the tightened wire and is the end of the wire system) allows one to account for the eventual wear and slacking that will occur over time as the system ages. This removes the need for further ajustment and provides for repeatability of action and deployment. The spring allows for a motorized system to 'ease' into a braking point without undue levels of pressure on the motor system because of high levels of near instant load changes. The spring loading of the tightening system is activated with the final positioning of the tensioning system ,and also allows for the slight inevitable stretching of the fibre backed screen material. Sorta like self adjusting valves on yer honda motorcycle... Once every year or so you may have to do a little adjustment, but not likely.

Now, some manufacturer should go make one....they have the facilities, I don't. It's too complex for a one-off, but is surely adaptable for maufacturing. A simple slat tensioned with a piece of twine is MUCH easier for a singular execution. Perhaps in the final analysis this will also prove true in manufacturing, as simpler is always better. (except in noth american politics where the objective is to fool the general public into accepting a corporate direction)

[This message has been edited by KBK (edited July 03, 2000).]

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