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Author Topic: Rear projection light blocking  (Read 7685 times)

Philip Roberts

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Rear projection light blocking
« on: August 06, 2010, 01:02:41 pm »

Does any one make an "off the shelf" kit for blocking light from hitting the back side of rear projection screens?

If not is pipe and drape the best way? Any setup hints? I'll be doing 3x 9x12's screens edge to edge once a week for the next 6-9 months so easy setup is a big plus.

Thanks,

Philip
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Philip Roberts
Director of Media Engineering
Pioneer Memorial Seventh Day Adventist Church
Berrien Springs MI

Luther Bell

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Re: Rear projection light blocking
« Reply #1 on: August 07, 2010, 11:07:44 am »

Are you looking at keeping the light from each screen from spilling or mainly for keeping ambient light out?

If it'll all be hidden, white drape would be better to make sure that as much light as possible makes it to the screen.

If you haven't checked yet, Da-Lite or Draper would be a couple companies to talk to.
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Luther Bell
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Kellen Tyburski

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Re: Rear projection light blocking
« Reply #2 on: August 07, 2010, 01:24:17 pm »

Questions:
Are the 9x12's setup backside facing windows?
What kind of projectors are you using?

One option would be to rent higher gain screens, especially because with 3 9x12's edge to edge, you could afford more of an acute viewing angle (with a high gain screen the brightness of the image increases to those seated in the center, and diminishes for those seated at the outside).

Depending on pricing though, P&D might be the more economical choice for the client, and I imagine (without seeing your room) that it would work pretty well.

K  
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Brad Weber

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Re: Rear projection light blocking
« Reply #3 on: August 07, 2010, 01:47:24 pm »

There does seem to be some potential confusion as to whether you are concerned about blocking ambient light to each screen or to the overall 36'x9' image and/or are wanting to block light between screens.  In either case, you do probably want to use a material with a flat black finish as you want to minimize any ambient or reflected light hitting the screen.

There are packaged rear projection systems using mirrors and enclosures but for direct rear projection and the size images being discussed, I think you're looking at something custom.

Since this will be something you apparently have to setup and break down for every use, you might also want to look at options to reduce the ambient light in the area in general rather than focusing just on blocking the light at the screens.
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Brad Weber
muse Audio Video

Mac Kerr

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Re: Rear projection light blocking
« Reply #4 on: August 07, 2010, 02:18:02 pm »

Kellen Tyburski wrote on Sat, 07 August 2010 13:24

One option would be to rent higher gain screens, especially because with 3 9x12's edge to edge, you could afford more of an acute viewing angle (with a high gain screen the brightness of the image increases to those seated in the center, and diminishes for those seated at the outside).


Don't forget that the higher gain screen also passes the ambient light better as well. A lower gain screen and a more powerful projector might help, but controlling the ambient light is the best answer.

Mac
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Mac Kerr

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Re: Rear projection light blocking
« Reply #5 on: August 07, 2010, 02:20:09 pm »

I think Brad has the right idea. Start with controlling the source of the light, and then use pipe and drape to isolate the screens if using P&D on the source wasn't enough.

Mac
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Philip Roberts

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Re: Rear projection light blocking
« Reply #6 on: August 07, 2010, 03:26:20 pm »

Mac Kerr wrote on Sat, 07 August 2010 14:20

I think Brad has the right idea. Start with controlling the source of the light, and then use pipe and drape to isolate the screens if using P&D on the source wasn't enough.

Mac


Mac, do you have a dimmer for the sun Smile.

I'm concerned with blocking ambient light. I'm fighting two lights sources. One is a big window high and behind the screens. The other is top/shoulder light for the video guys that comes down form a very high angle. As the room is used for other things I'm not going to get this light masked/shuttered out.

I called Da-Lite and they didn't have a kit to block the light.

index.php/fa/31885/0/
I've attached a pictures showing about where the screens will be placed. They will be well back on the stage, just far enough out so that I can project from behind w/o mirrors and such with a wide lens. They will be used to project a backdrop for a weekly program.

Being as this will be used every week and not being close to big rental houses I'd be looking to buy where ever we use.

We've not selected projectors yet, 10k's would be enough with out blocking the light but the powers that be are choking on the price of 3x 10k projectors. I'm hoping to block enough light that something in the 3-6k range will do the trick while still not spending so much on blocking the light that I could have gotten the brighter projectors for the same money.

Philip
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Philip Roberts
Director of Media Engineering
Pioneer Memorial Seventh Day Adventist Church
Berrien Springs MI

Mac Kerr

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Re: Rear projection light blocking
« Reply #7 on: August 07, 2010, 06:28:02 pm »

Since the windows are important and you can't cover them it seems like pipe and drape is your only chance. It is a PITA, but I have seen drape hung from frames like in the drawing below. You need the pipe cross members to support the drape so it doesn't sag into the projection cone. Use more or less as needed.

The shortest lenses I am familiar with are .8 ratio which means you still need about 10' to the lens, and about 3' more for the projector.

Mac

index.php/fa/31893/0/
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Brad Weber

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Re: Rear projection light blocking
« Reply #8 on: August 08, 2010, 06:35:33 pm »

To add to Mac's points, the picture provided makes it look like some of the seating is literally to the sides of the screens.  I don't know if the goal is to spread one image across three screens, to show three different images or to have two image with the same image on both outer screens (or some combination of these) but each would have limitations as far as viewing areas that appear to not include areas of the seating.  A high gain or narrow horizontal viewing screen would exacerbate this issue, you'd probably want a screen with as wide a viewing or half gain angle as possible.

The 0.8:1 lens, and a few projectors do offer shorter throw than that, usually require the projector to be on the centerline of the screen horizontally and vertically.  Your picture seems to show maybe 2-1/2' to 3' below the image, so with a 9' high image the projector centerline would need to be 7' to 7-1/2' above the stage floor.  That would probably require more than your typical cart.

With the kind of light shown and having no control over it, even a 10k lumen projector might be pushing it without any reduction of the ambient light levels.

The screen gain would not really matter in the sense that if both the projected light and ambient light are from behind then the gain affects them both and the contrast ration achievable would be based solely on the ration of the projector output to the ambient light level on the screen.

If you can tell us what you are trying to do then maybe there are some other options to explore.
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Brad Weber
muse Audio Video

Philip Roberts

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Re: Rear projection light blocking
« Reply #9 on: August 09, 2010, 01:02:39 am »

Brad Weber wrote on Sun, 08 August 2010 18:35


If you can tell us what you are trying to do then maybe there are some other options to explore.


The seating on the stage is unusual, it just was the most convenient image I could find on the web. The back of the stage will be empty when this is used. Just a band, (2-3 vocals, guitar, bass, misc percussion, piano, no drum set) or a single presenter in front.

The screens will be projecting one wide image, that will be used as a backdrop, I'm guessing mostly kind of abstract stuff. I'm just the tech guy and not the graphics guy. The audience is not expected to have to read off these screens.

Based on light meter measurements of around 100 lux on the back on the screen during the afternoon I calculated that a 10k projector would give about 10:1 contrast, I also mocked up the same brightness with a smaller projector on a fraction of the screen with good results. Program is late morning so that should help a bit also.

Thinking abit more about the pipe and drape: it appears that Rosebrand makes this, who are the other major players who have good prices?
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Philip Roberts
Director of Media Engineering
Pioneer Memorial Seventh Day Adventist Church
Berrien Springs MI
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