Torus and CRT - A Torrific Combo - Part 1 - AVS Forum
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post #1 of 276 Old 03-06-2005, 11:07 AM - Thread Starter
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I've had my new Torus screen up for a week now, so thought I share my impressions..

The screen was made by a local AVS' er - Semisentient (James) - James started a thread here:

http://www.avsforum.com/avs-vb/showt...hreadid=511816

This is part 1, because I still have to move the 1292 back to accomodate the wider Torus - the Torus is 2:1 (54" x 108") - currently it is set up for 16:9 (54" x 96") - I'll add any comments later once the CRT has been properly reconverged for the final 2:1..from what I can tell, I don't anticipate having any negatives when I go wider..

This is the 4th screen I have used with this same CRT - first one was a Studiotek 130 which was replaced with the same size Silverstar. I still have a Screen Goo behind the Torus, which I used for viewing while doing the blending stuff...

I haven't bothered doing a complete new reconvergence - just did the basics - lens adjustments for center and edge focus plus usual convergence on the grids..

Negatives

There is only one - due to the curvature in both directions - there is a curvature to the image - if you were to display a static image of a line across the width of the screen, the line wouldn't be totally flat - it would have a slight curve to it.
In moving video, this is not a problem and doesn't bother me.

I was initially concerned about corner focus - I had no problem using the zone convergence control to get good focus everywhere - so focus is uniform through out..

Positives

there are 2 significant advantages to a Torus:

A- Increased Brightness

Compared to the Studiotek/Screen Goo - the Torus is MUCH brighter - against the Silverstar there is only a small increase in brightness. I had originally intended to reduce my contrast - not to save tube life - but to get better focus and sharpness.. Brightness though is a one way trip - once you get used to a brighter image you won't like a duller one..

I expect that when I go to the wider screen the contrast will stay at the default 80, so no savings here...

B- Brightness Uniformity

This is the very first time that there is uniform brightness across the entire width!! This was a pleasant surprise - I thought it was a function of CRT to have it brighter in the center so you live with it..

Another concern was how would the Torus look if you don't sit dead center..I have 3 rows of seating - the screen was designed for the 2nd row where I normally sit. I experimented with tilting the bottom up and the top forward and ended up with the screen level. The brightness is very uniform from all seats and each of the 3 rows..

C- Colours looked great on the Silverstar and will look equally good on the Torus once the gray scale is redone for the Torus..It might be pyschological, but the Torus seems have slightly better image depth..

The Torus is a keeper and I already sold the Silverstar..

John
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post #2 of 276 Old 03-06-2005, 12:26 PM
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Yes, uniform brightness should be a major benefit of curved and toroidal screens. See e.g. my post about curved screens and uniformity.

I'd guess the bright spot you've seen in the center was a result of your high-gain screen, not the CRT. It was just a big hotspot. Did you see it with the Studiotek? A 1.3 gain screen shouldn't hotspot noticeably.

Sigh. I gotta build me a torus... :)
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post #3 of 276 Old 03-06-2005, 12:30 PM
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So what fabric did you use?
Is your CRT ceiling mounted?
I want to make a 4m wide torus, but can't find suitable fabric!

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post #4 of 276 Old 03-06-2005, 12:40 PM
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Quote:
Originally posted by dokworm
So what fabric did you use?
Is your CRT ceiling mounted?
I want to make a 4m wide torus, but can't find suitable fabric!
Let me jump in and answer...

The fabric is Vutec PearlBrite 3.1. We got it from AVS, price was $5 a square foot. Hopefully it hasn't gone up cause I'm building one for myself now. From what I remember it is available in whatever size you want (within reason I suppose...).

John's CRT is ceiling mounted.


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post #5 of 276 Old 03-06-2005, 01:36 PM
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So unlike a flat high gain screen you aren't losing brightness with ceiling mount vs floor mount?
So I'm looking at $500 of material then...ouch! I'd wanna get it right!

Is a higher gain material available?

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post #6 of 276 Old 03-06-2005, 01:49 PM - Thread Starter
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Quote:
Originally posted by garyfritz
Yes, uniform brightness should be a major benefit of curved and toroidal screens. See e.g. my post about curved screens and uniformity.

I'd guess the bright spot you've seen in the center was a result of your high-gain screen, not the CRT. It was just a big hotspot.


Did you see it with the Studiotek? A 1.3 gain screen shouldn't hotspot noticeably.
definately worse on the Silverstar - was also evident on the Studiotek - didn't assume it was really hotspotting like the Silverstar, but the sides were darker than the middle - enough that I would notice this..

John
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post #7 of 276 Old 03-06-2005, 02:25 PM
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Quote:
Originally posted by dokworm
So unlike a flat high gain screen you aren't losing brightness with ceiling mount vs floor mount?
So I'm looking at $500 of material then...ouch! I'd wanna get it right!

Is a higher gain material available?
How many square feet is your screen??

Clay:eek:

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post #8 of 276 Old 03-06-2005, 03:01 PM
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Well, 4m wide, so what is that about 13.3ftwide by 7.5ft high, so around 100 square feet I guess.
Go big or go home.

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post #9 of 276 Old 03-06-2005, 03:11 PM
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MC Maniac,
I have been waiting for this review. I am glad that you like it.

So, if my math is correct, then I am guessing there is about $400 into this screen not counting labor. That sounds like a good return on investment.

garyfritz,
Have you read this link http://archive.avsforum.com/avs-vb/s...ighlight=torus ?

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post #10 of 276 Old 03-06-2005, 03:30 PM
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Yup, just saw your reference to it a few days ago. MC Maniac, look at the first few pics in that thread. He did a simulation of what various screens would look like. The first few pics show the amount of hotspotting for several screen gains. Even the 1.3 has noticeable dropoff.
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post #11 of 276 Old 03-06-2005, 03:33 PM
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Quote:
Originally posted by dokworm
Well, 4m wide, so what is that about 13.3ftwide by 7.5ft high, so around 100 square feet I guess.
Go big or go home.
Go big, spend big. Sounds like a deal to me!
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post #12 of 276 Old 03-06-2005, 03:33 PM - Thread Starter
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Thanks for the archive link Eric..

This post was interesting:

Corner focus

Mike,

Have you tried using a Sony 1292Q? It was reportedly specifically designed for use with curved screens, causing corner focus difficulities with flat screens but making it a prime candidate for one of these babies...

---

As I have a 1292 and am very happy with the corner focus, I wonder now about this if you have a different CRT..

John
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post #13 of 276 Old 03-06-2005, 03:54 PM
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$5 a sq ft sounds very well priced, can this screen be used flat or curved, as in only horizontal curved.

When the Iceman was talking about spherical screens, what is a spherical screen. He also mentioned circular screens, would that be a horizontal only curved screen. How much curve should a 6.5ft wide screen need, difference between center and edges in inches, or would it depend on how many seat wide the viewers would be at.

Walter
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post #14 of 276 Old 03-06-2005, 04:13 PM
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I have a few more tips for anyone wanting to build this screen using the VuTek material mentioned here. The material is a bit translucent so you want to line the inside of your box with black felt or at the very least paint it flat black.
Also I read the thread that James did on this screen (very nice James) about using a contact switch to insure that the screen material is always in place. I have been running one of these for about 2 years and it is my experience that once the material find it's final place, it will not move. So the trick is to use a variable voltage wall bug for the fan and you will find that it takes very little voltace to "suck" the screen in. Mine stays on 24/7 and I haven't adjusted it in a year. And I only adjusted the voltage once before that.

John, also the lines you are putting on the screen are in fact straight, it just depends on where you are looking at then from. If you are perpendicular to the screen and at the same height as the line, it is straight. Took me about a week to get uses to the curve. But once I did, I will never go back to a flat screen. The gain in contrast is huge.

Also, for those thinking about this as a screen, the lens's on Johns 1292 are some of the best focusing lens's for a curved screen of this type. I use them on Marquee 9500's that are getting a curved screen. They focus the corners and edges very well and better than any other lens system I've tried.....and I have tried them all. But don't let that sway you away from a Torus. You will have a hard time seeing the slightly out of focus corners except for the desktop of a HTPC.

Nice going guys!!

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post #15 of 276 Old 03-06-2005, 05:11 PM
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As it works out, we didn't need the switch. I figured I would adjust the switch once the screen was under vacuum, but the screen ended up being at the correct depth without it. I guess the switch is now a backup should the screen stretch. Good news Terry that the material doesn't stretch even after being on for a year 24/7!

James

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post #16 of 276 Old 03-06-2005, 05:28 PM
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Atom didn't bother with a limit switch....

John and Chuchuf, now you guys have me wondering about my Barco 808 which has some hd-144 lenses coming.....

I just assembled my Torus frame yesterday. It had to come in before the room is fully enclosed.

James, nice work! What paint did you use with it?
LL
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post #17 of 276 Old 03-06-2005, 05:29 PM
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Hi James,

Did you use the calcs that Iceman used for getting the curve depth dimensions for both hor and vert. I believe his was 2m wide and 1m+ high and the depth was 200mm for the hor and 50 for the vert.
Or did you use another method to get the hor and vert depths in relation to the width and height.

TEDD, wow how big is that screen you're making.

Thanks

Walter
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post #18 of 276 Old 03-06-2005, 05:42 PM
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Walter, try "Wow, how narrow is that room?" :D

The screen box is 55"x95" while the room is only 113" wide. I expect it'll end up masked down to around 52"x92".

As for cost, it'll come in just over $400 (CDN). A real bargain!
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post #19 of 276 Old 03-06-2005, 05:55 PM
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Tedd, that sounds like a great price, I was thinking of doing a 6.5 wide (90" diag). Where did you get it and how much did you pay for the screen, are you using the Vutec pearlbrite 3.1. What formula did you use to calculate the depths of the curves.

Walter
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post #20 of 276 Old 03-06-2005, 06:05 PM
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Terry, what lenses does the 1292 take? HD-144's, isn't it? That's what I have in my XG so it would be nice if those were good corner-focusers on curved screens...
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Talk to Jason at the AV Science. It is shipped from the factory so you'll get dinged with duty and all.

I am basically following Atom's lead. After seeing his screen in action, I didn't feel any need to stray from his well thought execution . I used a piece of cheap MDF door trim to do the curves. 3.5 inch deep vertical curve and 7.5 inch deep horizontal curve. Jig sawed them out and finished with a belt sander.

Gary, I think the 1292Q uses HD10F. As Chuckuf mentioned, it took a computer desktop image to see the corners weren't perfectly focused.
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post #22 of 276 Old 03-06-2005, 06:15 PM
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Quote:
Originally posted by WTS
Hi James,

Did you use the calcs that Iceman used for getting the curve depth dimensions for both hor and vert. I believe his was 2m wide and 1m+ high and the depth was 200mm for the hor and 50 for the vert.
Or did you use another method to get the hor and vert depths in relation to the width and height.

TEDD, wow how big is that screen you're making.

Thanks
Walter,

We actually based the curves on John's screen on the curves on Atom's. We just made the horizontal curve a bit deeper because of the added width. There is a method to trace out curves using string, but that usually ends up with deeper curves than you may want to go with. I suggest using curve depths based on an already built Torus of the same size.

James

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post #23 of 276 Old 03-06-2005, 06:20 PM
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How was the edge to center focus. I've read a few posts regarding there being no way to focus the CRTs edge to edge corner to corner with a toroidal screen.

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post #24 of 276 Old 03-06-2005, 06:21 PM
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Quote:
Originally posted by Tedd
Atom didn't bother with a limit switch....

John and Chuchuf, now you guys have me wondering about my Barco 808 which has some hd-144 lenses coming.....

I just assembled my Torus frame yesterday. It had to come in before the room is fully enclosed.

James, nice work! What paint did you use with it?

Lookin' good Tedd!

I just used flat black spray paint. I first did a coat of brush on flat black, but found it still had too much of a sheen. For the inside I really recommend black velvet given the Vutec material's translucence.

I think 1292's come with HD-10 lenses. At least mine has 'em.

James

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post #25 of 276 Old 03-06-2005, 06:27 PM
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Thanks for the info guys

Walter
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post #26 of 276 Old 03-06-2005, 08:31 PM
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Art,
The G90 and 1292 use the same basic HD-10 lens assy (HD10f) and I can tell you from experience that the corner focus, while not as perfect as the center on the G90 is pretty close. Unless you are putting up a computer desktop or the EM focus pattern you won't see it when watching video or film.

Tedd, I found the HD144's to be one of the better lens's to focus on a Torus. Better than the XG/LC and G70 lens's. Really the only ones I hadn't tested to any degree are the HD-8's.

I've got to say that I am very excited about the number of folks who are delving into building a Torus screen. Mine two years later still blows me away every time I look at it. Another advantage is that the viewing angle is very large, something I initially didn't expect.

Terry

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post #27 of 276 Old 03-06-2005, 08:39 PM
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Makes me wonder how that Vutec material can have a 3.1 gain if it's so translucent. If that much light is leaking through, how can so much get bounced back?
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post #28 of 276 Old 03-06-2005, 08:46 PM
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I didn't say it was _so_ translucent, just that some light does leak through. And this can manifest itself in a very dark scene where there is something small but bright (the night sky with the moon as an example). If you have a light or white inside of the box, it will try and send some of that light back through the screen. Whereas if that light is killed in the box with something tark, you don't see this.

I would really like to try the Stewart 2.8 material that was designed for this application if it ever becomes available again.

What are ya'll (southern for youze guys) doing for the black border on these screens??

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post #29 of 276 Old 03-06-2005, 08:54 PM
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Let me also give you some numbers. When I built mine I used 106" x 60" and the drop is about 7" on the horizontal sides and about 3.5" on the vertical sides. If you measure back to my CRT face, you will find that the radius I used is much longer than the actual distance to the CRT face (which is what hypothetically you should use). I was concerned about this but wanted to reduce the curve as much as I could get away with but still get a good picture.
Well, it works and I get no hot spotting (or sould I say even hot spotting over the entire screen) and no color shift. None.

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post #30 of 276 Old 03-06-2005, 09:28 PM
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Quote:
Originally posted by Chuchuf
Art,
The G90 and 1292 use the same basic HD-10 lens assy (HD10f) and I can tell you from experience that the corner focus, while not as perfect as the center on the G90 is pretty close. Unless you are putting up a computer desktop or the EM focus pattern you won't see it when watching video or film.

I've got to say that I am very excited about the number of folks who are delving into building a Torus screen. Mine two years later still blows me away every time I look at it. Another advantage is that the viewing aghle is very large, something I initially didn't expect.

Terry
Great to hear . Have any of you ever attempted to produce a rigid torus ?

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