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Adding gain to a very LARGE industrial screen  

post #1 of 5
Thread Starter 
Hello,

I am writing this message on behalf of a friend of mine. He is the director of the Burke Baker Planetarium in Houston, TX.

They have one of the most impressive video display systems in the world. Using 6 Barco 1209's they create a 2200 X 2200 image that covers an entire 180 degree hemisphere. Using special software they divide the 2200 X 2200 pixel image among the 6 projectors to create on continuous image that fills the 50' diameter dome. With properly aligned edge blending, the viewer can hardly tell that 6 projectors are at work to make the image.

The show is quite impressive. If you are ever in the Houston area, I recommend you come to see it.

However all is not perfect, the problem they are having is cross talk between projectors and a general lack of but from the projectors themselves (even six 9" gun projectors isn't enough to brightly light a complete 50' dome). This situation is not helped by the fact that the dome surface is a flat white (i.e. no gain). Each projector is mounted along the bottom lip of the dome, they project across to the other side to produce their own portion of total image. The screen surface angles most of the light down, but I would say at least 35% or more is reflected upwards onto other sections of the dome.

As an illustration, star fields look great - the projectors have an easy workload so the stars are nice and bright. There is very little crosstalk either because the image overall is mostly black.

But an image that is mostly white with a only a few dark areas poses a tremendous workload on the projectors and causes dark spots to become washed out with all the light scattering going on. the contrast ratio takes a real hit and the resulting image isn't all that impressive.

A good solution to both of these problems would be to add some gain to projection surface this would cause more of the light to be reflected back to the viewer instead of being bounced around in the dome.

Implementing the solution won't be very easy however. First off, no company I know makes a 50' perforated hemisphere screen for any reasonable amount of money (for a variety of reasons the dome is and needs to remain about 15% small holes). If they could find some glossy white paint to use that might be an option, however, this would probably expose the seams used to create the dome.

What they need is a clear paint to be applied, that would add a little luster (or gain) to the surface. They need about 1.5 or higher but with a fairly even results but not necessarily perfect. Please note that the image surface is on average about 30 to 40 feet from the viewer so perlescent elements in the paint might not be all that objectionable from that distance.

They are a non-profit organization, but they have small budget for this improvement somewhere in the $10K range.

Any Suggestions?

Thanks for reading,

-Mr. Wigggles

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post #2 of 5
I'm sure I could deliver them the paint product, but there are other problems to consider. The point at which the images meet would have an even more noticable problem, with regards to the edges of each being too dark, and causing the 'definition' of a screen width to easily enter the mind of the casual observer. (once you get away from the low gain, the directivity of the surface will cause there to be a more noticable level of darkening at the edges. The projectors have their own problems in this regard, and the high gain paint will excabarate this) There is also pre-thinning of the mix so that when spraying, the holes are not obscured. High gain paints require a very steady and controlled hand and brain. It is like trying to see exactly the outline of sheep in a blizzard... at night. Experts only, please. Imagine what it would be like to try and chack your spraying consistency on a curved surface, spraying white paint on a white surface. Visual cues for coverage are screwed....

None of these problems are insurmountable though. The big thing is whether it can be finalized in the buget that is considered. When you start to get into areas of experimenting, when the meter is running.....

How many square feet? how big are the holes? How far apart are they? Consider the mass of the paint, as a structural consideration. Consider safety codes re: product type and origins. (liability, and validity of insurance coverage)

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[This message has been edited by KBK (edited 10-18-2000).]
post #3 of 5
Thread Starter 
KBK,

They have an edge blending algorithm to take care of the hot-spotting CRT's generally have. The curve screen would help hotspotting regardless. If the gain is kept somewhere in the 1.5 range we probably won't have a problem.

I don't think the mass of the paint will be a problem. The dome is fairly thick aluminum.

The holes are 15% of the surface and are aproximately 5 mm im diameter. (From 30 feet away they are not visible.) I doubt that even the thickest coat would cause a problem.

The surface area is about 3000 sq feet.

As I mentioned before, the paint will more than likely have to be clear not white. At the seeams of the dome, a sheet of black paper is placed between the two layers. This makes the dome appear seamless when in actuality the dome has plenty of seams. Painting with white paint would color these strips white. It might possible to paint with the white paint if a roller is used - the curve is slow enough that a roller would be difficult but possible

Speaking of rollersThey would also like to paint with a roller if possible in some locations. There is plenty of stuff behind the lower portion rim of the dome that would be a real chore to mask and/or relocate.

I have never heard of a paint being a fire hazard. If you know something I don't please let me know.

One last thing, the gloss coating would have to have a reasonable life span 10+ years and be able to be cleaned in a light fashion every 3 years or so.

With the above constraints if you still think you can come up with a product, please let me know. We can arrange to get some sort of sample.

Looking to hear from you KBK (or anyone else who has other info).

-Mr. Wigggles

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post #4 of 5
The product will have to be sprayed if it is to work at all. Rolling would be nice, but it won't work. It will not have the desired effect at all.

I am basically using that exact product right now.

If you wish to discuss further, then e-mail me.

Here, let me add this:

Curators of museums sometimes have to repair the frames of 2-300-whatever year old paintings, in period era frames. Sometimes the guilding of the frames is falling apart. Sometimes the carved wood pieces break off, and have to be repaired. So, a craftsman is brought in to carve an exact replica of the missing piece. The craftsman does so, and paints the new piece and glues it in. Lots of difficult and time consuming work to fix a valuble frame.

Recently, some of these folk have turned to using some of this paint product in a GEL form to replace the wood carving phase entirely. They mix up the requisite color in the GEL form, and place the gel in the frame, in the area of the missing carved piece. The craftsman shapes the gel to the desired shape, and then lets it dry.

There is no noticable loss in mass, and/or color shift through the drying. The match they achieve in 'covering up' the bad area is better than before (with the carved, painted wood piece) and the GEL form paint does not loose color fastness over time. (well I am sure it DOES, but what time period are we talking about?) When I was told this, I thought, 'now THAT'S impressive...'

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[This message has been edited by KBK (edited 10-23-2000).]
post #5 of 5
Thread Starter 
KBK,

Is your email address still valid?

Looking forward to hearing from you.

-Mr. Wigggles

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