Projecting an image onto two spheres 3.5 ft in diameter - AVS | Home Theater Discussions And Reviews
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post #1 of 17 Old 08-30-2014, 04:44 PM - Thread Starter
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Projecting an image onto two spheres 3.5 ft in diameter

I am trying to build two hemispherical screens that will be suspended above a live band. The best way I can think of to do this economically is buy 2 beach balls from beachballs.com, blow them up, and wrap them in some sort of spandex and pull it tight around the ball, and crimp it at one end that would hang at the back, facing away from the viewer. To hang them, it would need to have some sort of loop or string attached to the top, and I definitely don't want any seams to show up on the projected surface, which is about 165 degrees. I've been going through a few threads on here and there seems to be a ton of fabrics I can choose from, and was wondering if someone could point me in a direction. Spandex? Lycra? Nylon? White? Grey? I know that white or sheeny fabrics can have screen gain , but I can't quite imagine what would happen if the screen was a sphere, or if I should be worrying about hotspots at all. If it's a sphere. the amount of screen that is aimed right at the projection is less than it would be if the screen was flat.

The projector is a Viewsonic PJD6553W. It's BRIGHT (3500) lumens and looks pretty clear. The resolution is 1280x800 which isn't the best, but since I'm mainly projecting output from Resolume Arena, I keep the resolution at 1024x768 to keep my frame rate up, so the resolution won't matter in the long run.

Thanks for reading!

Edit For reference:
Whole image will be 15 ft wide
projector will be 18.2 ft from the spheres
spheres are 3.5 ft in diameter, and 6 ft apart

Last edited by loganwexler; 08-30-2014 at 04:53 PM. Reason: added some measurements
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post #2 of 17 Old 08-30-2014, 04:51 PM
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With the projector "fighting" with the spotlights and other lighting on stage, ImO your biggest problem is the lack of light output from the projector

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post #3 of 17 Old 08-30-2014, 04:55 PM - Thread Starter
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We can turn stage lights off, but there are still neon, bar lights, lights from outside to worry about.
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post #4 of 17 Old 08-30-2014, 04:57 PM
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Grey material will help a tiny bit but those ambient lights are so going to kill the details projected to those balls.

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post #5 of 17 Old 08-30-2014, 05:12 PM - Thread Starter
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Do I need a more powerful projector? Or do I just need to be closer? This is something that I want to set up in many different venues. The videos are blurry vhs-esque color collages and stuff, the details really aren't so important. I just want it to look cool.
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post #6 of 17 Old 08-30-2014, 05:34 PM
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How far are the projectors going to be from the balls? How large are the balls? Also how are you going to process the image so the projected image won't be all stretchy and out of focus?

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post #7 of 17 Old 08-30-2014, 05:54 PM - Thread Starter
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Using the calculator on projector central, http://www.projectorcentral.com/View...ulator-pro.htm

projector will be 18-21 ft from the front of both spheres. The image/screen size will be about 15-17 ft wide.
spheres are 3.5 ft in diameter, and 6-8 ft apart. This leaves 1 foot on each of the outer edges of blank space, so I could hang the balls a little further apart, and also get a little closer if I need to.

For the distortion: In Resolume Arena, I can create spherical meshes so that it accounts for the spherical screen and does not distort too bad. Here's how: http://resolume.com/manual/en/r4/output That accounts for the sphere shape and the stretching, but doesn't account for the problem with focusing on a sphere thats 18ft away and the edges which are 1.6 feet further back. I guess I would have to approximate and try to get it to a happy medium. Or maybe make curved screens that aren't full hemispheres. Like a contact lens shaped dome attached to a wood panel, with not such a deep curve.

Since we are a touring band, I'm trying to build something that I can apply to many venues. The way I imagine it, I will set up the balls, and then set up the projector, and then adjust the resolume output and manually match it up to the spheres, since with every change in throw distance, the size of the projected circles would change. Bars, venues, and art spaces have all different layouts, so I'd like to be flexible.

Last edited by loganwexler; 08-30-2014 at 06:00 PM.
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post #8 of 17 Old 08-30-2014, 06:23 PM
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Thanks for the info. After reading all that, my concern goes back to the lack of brightness. You are really pushing the limits of the that projector even in complete darkness. You may have to do a double-stack to get it anywhere near the brightness level you need.

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post #9 of 17 Old 08-30-2014, 06:26 PM - Thread Starter
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Is a doublestack 2 projectors? Before I get another, I'm going to try it with this one, and if it doesn't work I can sell this one and get a brighter one. If i'm low on brightness, shouldn't I get the fabric with the most screen gain/the sheeniest/white instead of grey?
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post #10 of 17 Old 08-30-2014, 06:28 PM
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Yes. My apology for not clarifying.

With double stacking you will get about 50% extra brightness (not double the brightness) of a single projector.

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post #11 of 17 Old 08-30-2014, 06:39 PM - Thread Starter
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I have an optoma ep727 http://www.projectorcentral.com/Optoma-EP727.htm
It's a different size, way different throw ratio, so they would not be able to be the same distance from the spheres, but I could probably make it work somehow. I think I'd rather not have to deal with setting up two though, and if this viewsonic doesnt work, ill just sell both and get a bright one. Thanks for all of your help.

Also, I edited my last post, did you see the part about grey vs. white. Since my projector is not THAT bright, don't I want the most reflective surface? Like white spandex, maybe a little bit sheeny?
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post #12 of 17 Old 08-30-2014, 06:42 PM
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The problem with reflective surface, they also reflect ambient light. By having a grey colour, the image will stand out more albeit slightly dimmer. You can try shiny grey spandex material, it will be grey but with a positive gain as opposed to nylon grey (grey but with negative gain).

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post #13 of 17 Old 08-30-2014, 06:55 PM - Thread Starter
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Awesome. I guess the factor I haven't grasped is just how much the light dissipates over distance. I had the ViewSonic thrown about 12 ft from a painted wall, semi gloss paint, and the ambient light in the room was just about the same as the venue I have in mind where I will first test this. It was pretty perfect, but I guess I don't have a feel for how much dimmer it gets when you add another 8-10 feet to the throw distance. From what I gather, it's substantial.

Another scenario, I could throw it at 15 ft, and have a 12 ft image, have no space on the outer edges, and then have only 5 ft between the balls. That could be brighter. It's just that, I may have to strap a ladder to a support beam and strap the projector to the ladder, run a long hdmi cable back to where the computer is, since 15 feet from the stage is going to be where the people are standing. Being further back, or being able to get further back, would be a great help and I guess I'm gonna need more power for that.
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post #14 of 17 Old 08-30-2014, 06:58 PM
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If you throw it at 15ft then it will be more likely that it's going to work for your needs.

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post #15 of 17 Old 08-30-2014, 07:11 PM - Thread Starter
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That sounds good, I'll just plan on rigging the projector super solid and get a long hdmi cable so that the computer can be at the back, and the projector kinda above the crowd.

Now for a whole new series of questions. Using Cargo straps to strap the projector to a ladder and the ladder to something else. Maybe some sandbags to put on the feet of the ladder? Or maybe there is a very artful way to hang it? What kind of gear could I have on hand to improvise a different rigging at every venue?

Straps
Tape for taping hdmi cable to the floor
a ladder
a sandbag or two
some sort of hanging bracket?
some nylon rope?

EDIT: Just want to say, this is the most helpful anyone has been on any internet forum about any topic. Kudos to you.
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Last edited by loganwexler; 08-30-2014 at 07:39 PM.
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post #16 of 17 Old 08-30-2014, 09:54 PM
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Your rigging seems to be okay. Use gaffer tape for your HDMI cable. How long of an HDMI cable you'll be using? You may need an HDMI extender if it is longer than 30ft.

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post #17 of 17 Old 08-30-2014, 11:07 PM - Thread Starter
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If that's the case, I'll go with a 25 footer. I can't imagine a scenario where we need it longer. I'll get back to you and let you know how it goes.
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