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Torus for blend setup
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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Wed May 28, 2014 9:32 pm    Post subject: Reply with quote


        Register to remove this ad. It's free!
I have a limited budged and can't pay such a price. The only things i can invest are brain and time.
Yes, little pocket-money too. But not several hundreds for a silver (aluminum) plastic foil.


It may be easy to take some cans of aluminum or zinc spray and paint whatever surface with it.
But, there is more to achieve than brightness. It must reflect every color delivered by the projector.
So if the color "response" is bad, one can tweak the 6500k menu for days without getting it right.
If i could trust colorimeters, i would get one and use it on different projection surfaces, maybe using
the color corrected NEC here with one or more sample pieces of commercial fabric and compare the
results to self-sprayed surfaces.
But i wanted to buy a colorimeter. And many of those reviews at amazon told me, that it would only be luck
if the measurements are right.
And i know no one near by or even further away who has a colorimeter, maybe would lean it to compare measurements.
These things are highly suspect to me. But, in some months i need to get one.
Can't imagine a blend would be possible without it.
On a single projector setup, it works using your eyes to correct colors. More or less.
But if you have to set two projectors on exact the same colors for they will produce a picture half by half together...
as said: can't imagine it would work without color measuring equipment.
Tell me Nash, how did you do that? Ah, and how big is your screen? What gain?
Did you measure lumens on it while having the 8" blend set up?

I have developer some ideas about building a rigid torus, but before i tell you these, i will think further into detail.
And it would be contra productive. If i tell you these now, we'll only talk about them and no one will tell other ideas.
So do you know, how a rigid torus can be made?

For those of you, who have expensive screen material: I don't say that these aren't good. Not meant as an offense.
But i think i can go cheaper, maybe it will work, maybe not. But it will surely be much more work.

Thanks for your help guys and good night.
Julian

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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Fri May 30, 2014 8:47 pm    Post subject: Reply with quote

Let's talk a bit about radii. I have a 3.12x1.75m screen, approximately 3.5m viewing distance (will be variable between 3 and 4m)
and the viewing distance is 1 to 1.5m wide.
Each projector projects 1.95x1.75m. Lenses are HD8B or (if i get them) HD 145.
Projector distance ... i would calculate these, but don't find the specs of the lenses.
I believe it was projector distance= 1.2x (image width+238mm) for HD8B
and 1.144x (image width +236mm) for HD 145.
Correct me if im wrong.
So projector distance will be 2.62m for HD 8B and 2.5m for HD145.

How do i get the desired radii? Calculate or guess them?

Regards, Julian

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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Sat May 31, 2014 11:46 am    Post subject: Reply with quote

If i use the torus calculator i get a depth of 12.5inch (31.75cm) in the middle.
Numbers entered: 122.8inch (312cm) wide, 69.1inch (175.5cm) high, sitting distance 138inch (350cm),
width of viewing area 40inch (100cm).
This viewing width is rather tightly calculated and my room does only allow me about 20cm of screen depth (measured overall!), so if i double the viewing width, i get half the depth.
Width of viewing area 80inch (200cm): 4.81inch (12.21cm) horizontal depth and 1.53inch (3.88cm) vertical depth.
These numbers are the cuts in the frame. The middle would be 4.81+1.53=6.34inch (16.1cm) deep.
Do i get these numbers right?
Are they reasonable? Is this the way you would do it? There are guys here who build several tori.
Is this a good point to start with? Remembering that the screen surface coating will play a role too:
How much gain would these curvatures allow without hotspotting? Or is it that way, that any curvatre eliminates hotspots?

Regards Julian


12.206cm=4.81inch, 3.88cm=1.53inch. I forgot to add this in the picture.

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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Mon Jun 02, 2014 8:25 pm    Post subject: Reply with quote

Come on guys, i have everything ready to start building.
The frame is done so far and i am about to cut the radii in it.

Did i provoke someone? If so, i'm sorry for it. That thing about screen fabric is nothing personal against anyone.
Please help me with the radii.

Thank you, Julian

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garyfritz




Joined: 08 Apr 2006
Posts: 12021
Location: Fort Collins, CO


PostLink    Posted: Mon Jun 02, 2014 9:48 pm    Post subject: Reply with quote

Didn't annoy me, I just don't have a lot to offer. When I get a chance I'll look closer at your questions and see if I can come up with any intelligent suggestions.
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Spanky Ham




Joined: 22 Mar 2006
Posts: 5643
Location: Comedy Central


PostLink    Posted: Tue Jun 03, 2014 2:53 am    Post subject: Reply with quote

Are you doing a hard Torus?
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garyfritz




Joined: 08 Apr 2006
Posts: 12021
Location: Fort Collins, CO


PostLink    Posted: Wed Jun 04, 2014 2:44 am    Post subject: Reply with quote

If you create a curve on your screen that forms an arc with its center at the viewing location, it will try to focus all the light at that spot. It will also create a very deep curve in the screen. You generally go with much shallower curves, which don't focus all the lights in one place, and thereby allow for a wider viewing area. Beyond that, I don't remember or didn't know much more detail. I do remember that the curves are not critical. A wide range of curves will work, it just affects the size of your viewing area and the resulting gain.
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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Wed Jun 04, 2014 6:46 pm    Post subject: Reply with quote

Seems i didn't send my last post.
@Spanky: Yes i am doing a hard torus.

Quote:
Didn't annoy me
Thats most important to me.
Ok, the thing about wider range of curves is known.
What made me insecure was the following:
If you draw the optics of the setup (and i did everything with the numbers i know and those have to be right)
you end up with some of the light reflected to outside of the viewing area. If you draw a smaller radius, the light gets more focussed.
But not everything to one place. That is not possible with a CRT and not at all with two of them.
So i wanted all the light at least focussed to the viewing area (which is drawn 2m wide, wider than it will be in reality).
The problem that i have in mind is not that it won't be bright enough, but that some of the primaries will give more light than others.
In fact, that the color won't be the same all over the screen.

See the outer reflected light beams. They go outside the shaded viewing area.
But 700 cm /23ft is too small. The curve would get too deep. I did now cut radii of about 860cm (21.2ft) in the frame i already build.
Hope it works good.

Just to show what i mean, radius is 7m. Now with 8.6m the outer light beams form a bigger angle. They go further away from the seating area. Don't have a pic of that, sry..



Regards, Julian

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garyfritz




Joined: 08 Apr 2006
Posts: 12021
Location: Fort Collins, CO


PostLink    Posted: Wed Jun 04, 2014 8:17 pm    Post subject: Reply with quote

If your screen was a mirror, it would work like that. You would have major problems not only with the different colors, but with the two projectors. You'd see reflections of the two projectors in totally different areas.

Since it's not a mirror, it disperses the light in a cone. A 1.0-gain fabric would disperse it almost uniformly in a hemisphere. With a high-gain fabric (which you need with a torus), the cone is much brighter in the center of the reflection than farther away from the center. It's between the 1.0 hemisphere and the mirror's perfect reflection. You'd see each projector's bright spot in a different location, though the curve would reduce the effect of that (by spreading the reflection of the bright center area, spreading the hotspot).

Depending on how high the gain is, you may see color issues because of the separation between lenses. But I wouldn't worry too much about that. As long as you stay under about 3.0 gain you're in well-understood territory and we know it works OK.

I'd be a lot more worried about the distance between the projectors. I don't know of anybody who's tried a torus blend so I really have no idea how it's going to work. It's very possible that e.g. the blend might look perfect from the left chair in the sweet spot, but it looks mismatched from the right chair. That's the thing that really concerns me about your project.
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Spanky Ham




Joined: 22 Mar 2006
Posts: 5643
Location: Comedy Central


PostLink    Posted: Thu Jun 05, 2014 3:32 am    Post subject: Reply with quote

If you want to try it, then you could try to make a white mirror. You could paint the screen white with your version of Behr UPW in high gloss. Put on multiple coats. You would then have to sand and buff it to a mirror finish. You do this by sanding it with progressively finer grit sandpaper. There are a couple of fine grit sandpaper manufacturers. I like Mirka Abralon up to 4000 grit. Next you could put on an opaque material that was see through like a rear projection screen material. The other way would be to put on another five or so coats of a clear gloss paint and run the grit again. This time you would be stopping at around 1500 or 2000.

This is just a theory I have had, but I think it would work.
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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Thu Jun 05, 2014 8:19 am    Post subject: Reply with quote

Hey Gary, Thing is i know that it won't be a mirror.Even not planning one.
But how else would you draw the reflections? The screen will partially reflect and partially absorb the light.
So the reflection angles describe the visible light. If the beam Points towards the Viewer, that area will appear bright,
darker otherwise.




Quote:
You'd see each projector's bright spot in a different location, though the curve would reduce the effect of that (by spreading the reflection of the bright center area, spreading the hotspot).


And to get a perfect uniform Picture, there is one right radius. But how to calculate it? I did it by drawings, and hope i did it well.

Quote:
Depending on how high the gain is, you may see color issues because of the separation between lenses.

Yes, but my Problem with that is as you can imagine: I don't know how high my gain will be.

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garyfritz




Joined: 08 Apr 2006
Posts: 12021
Location: Fort Collins, CO


PostLink    Posted: Thu Jun 05, 2014 2:50 pm    Post subject: Reply with quote

Yes, I know you know it won't be a mirror. I was just being pedantic and explaining the range from mirror to 1.0 gain. Very Happy

I'm not convinced there IS one right radius. You're going to have different reflectivity for the two projectors at different points on the screen, and different radius selection won't change that. And that's likely to mess up the perfect match needed for a good blend.
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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Thu Jun 05, 2014 8:54 pm    Post subject: Reply with quote

Hey guys, i wanted to wirte more in the last post, but i was at school and the teacher came in, stared at my screen saying something like "bla blabla!!"
So i had to finish my post and listen to his bla bla...

Back to topic: I agree with you. There cannot be OEN right radius for a given setup with one or more projectors and a given seating area.
Mathematically there must be one perfect solution, but again you're right, these are not mirrors, and even from outside my drawed lines, you will see a picture
on the screen. It will be dimmer than in the sweetspot, but how dim will depend on the screen gain.
There must be a range of good radii for a given setup, not one, but a range that works.
Otherwise, it would not be possible to build and sell tori. You would have to construct every single torus with other radii.


I did now the wooden frame, cut the 8.6m radii in it and build a strutting to make it more stable.
Put backing plates of 3mm MDF behind it and thats it for now.
Tomorrow i will hopefully find time to fill everything with insulating styrofoam.
If there is time, build a 2m long curved "knife" to cut the radii into the styrofoam and after i did that,
it's time to get some glass fiber board and epoxy resin.
That will be the final lamination to watch movies on.
Yes, sure, there will be a coating. Zinc or aluminum paint, didn't decide it yet.
Some guys in a german diy forum told me, they used such paint, but you have to have good spraying skills.
Otherwise, the picture will not be as uniform as desired.

So long for now, Julian

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hansilili




Joined: 09 Mar 2007
Posts: 302
Location: Köln, Germany


PostLink    Posted: Thu Jun 12, 2014 7:41 am    Post subject: Reply with quote

give us some pics, please!
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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Sat Jul 05, 2014 11:05 am    Post subject: Reply with quote

So, here it is.

The screen will be 312x175.5cm. Thats 10.24x5.76ft. I increased the height to 180cm, that should make it easier to integrate
a masking.
I bought some 4m long 10cm wide slot and key boards (no keyboards...) and glued them together ending up with 20cm wide boards.
Sliced the outer slots and keys down.
Cut them to the desired length and screwed them on 3mm MDF (the backplane).
Strengthened the box with some square wood (in the corners) and some diagnoal slats.
The "H" with two horizontal spokes were removed again earlier, because they would have sticked out the screen
after finishing it.

Then it was time to cut the desired radii. I had decided to use some 8.6m wide, so a 8.6m dividers was build.
I used a thin wire and a marker for this.
After cutting the radii with a jigsaw, mounting the Styrofoam blocks could start.
The box wasn't rigid at all at this time. It got rigid after gluing the Styrofoam into place.
I bought that Styrofoam as "isolation" material for house walls.
It's 1mx0.5m. I have 12, 8 and 6cm thick pieces. I used some very cheap silicone to glue it onto the backplane.
But, silicone can't be cut with a hot wire, so i had to use something else for the second layer of Styrofoam.
"Bauschaum", maybe to translate as "expanding foam", let's call it polyurethane foam was the key.
I tested it. It can be cut with a hot wire and glues Styrofoam very well.
Expansion was avoided by letting it expand, before the Styrofoam was set in place.
Just apply it, wait 1 or 2 minutes and then set the Styrofoam block you want to glue in place.
Weight down the block with a wooden plate and some heavy stones.

Thats it so far.

Any questions?
Regards, Julian

Gallery


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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Sun Oct 05, 2014 12:18 pm    Post subject: Reply with quote

Any further interest in this? I have some more pictures, today it's painting day...
Regards, Julian

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Spanky Ham




Joined: 22 Mar 2006
Posts: 5643
Location: Comedy Central


PostLink    Posted: Sun Oct 05, 2014 4:24 pm    Post subject: Reply with quote

I am always curious with what people come up with.
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AnalogRocks
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TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Sun Oct 05, 2014 7:55 pm    Post subject: Reply with quote

tschaeikaei wrote:
Any further interest in this? I have some more pictures, today it's painting day...
Regards, Julian


YES! You are just slow on the updates Very Happy

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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Sun Dec 07, 2014 1:01 pm    Post subject: Reply with quote

Yes, i'm slow, not only on the updates, but also on finishing the screen.
Here are some pictures.


First method to cut the styrofoam. Heated curved "knife". It did work, but you see how good it worked.
The knife bend, melted foam burned itself into the surface...



Next try: Belt sander (Chuck Norris edition). Also curved, tool me a week to build it (like the knife did, too).
Worked very well.
The second pic shows the belt sander on the bad burned surface theat was left by the knife before.


This is what the belt sander did. Surface on this picture: Styrofoam with lots of gypsum (to fill the holes).
After sanding, leveling with gypsum, sanding, leveling for a few (or more than a few) times, we applied GFK to it.
450g/m˛ heavy biaxial fiberglass fabric in two layers and 5kg epoxy resin, it looked like this.


More fiberglas pics in the last link.


The Surface after finishing epoxy and filling with 2k body filler and filler. I don't know the exact english words for these,
German: 2k Spritzspachtel and 2k Füller (normally to use for car painting).
Sanding by hand and by a machine.

Here are even more pictures.

belt sander
screen at the beginning and after finishing filler
tests with aluminium and zinc spray
Doing the fiberglas/ resin work

Oh and i did start with a new hobby, radios. Here are some.
Gallery

Regards, Julian

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tschaeikaei




Joined: 08 Apr 2013
Posts: 489
Location: Germany/Saarland


PostLink    Posted: Sat Dec 13, 2014 10:46 am    Post subject: Reply with quote

Did anyone ever order and test a high gain silver screen at alibaba.com?
There are many cheap and interesting materials in the gain 2,2-3,8 range.
Mainly gains above 3 seem to fit for my screen.

Regards, Julian

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