# Cool projection enlargment trick



## LD4Life (Jan 20, 2008)

Just thought I would give you guys something to look forward to in this category. We are doing a production of _Sunday in the Park with George_ by Sondheim/Lapine right now. Most of our set consists of a 34' wide deck raked at 4.5 degrees. Behind that is a scrim-like screen stretching the full length of the stage. The backdrop for the show is George Seurate's _Sunday on the Island of Grand Jatte_, which is projected across the entire 34' of deck length. A graphic artist has edited the painting so that figures are "painted" on the scrim as the artist "paints" them on his canvas. Since actors are in front of this scrim, we are accomplishing this through rear projection. The catch is that we only have 12' of space between the rear wall of the stage and the srim, and a projector with a lense that shoots at about a 45 degree angle out to each side as the image progresses. After quite a bit of calculating and brainstorming, we have rigged a mirror system to enlarge the image to it's full 34' spread. I look forward to posting the specs for how we did this later on so that anyone else who has a small stage and a need for a large projection can use it.
Play on!


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## Footer (Jan 20, 2008)

Mirrors work rather well, but they do cut your overall output. If you can get a hold of top coated mirror (mirror that is on the outside of the glass, not the inside) you will be able to keep relativly the same brightness. There is also a good thread on this that went up a little over a year ago. 

http://www.controlbooth.com/forums/showthread.php?t=4359&highlight=mirror+bounce


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## museav (Jan 21, 2008)

Using mirrors can work, but is not always as simple as it seems. I have worked with both packaged mirror systems and custom built mirror systems, including many horizontal mirrors like you seem to be considering. As Footer noted, there is some light loss, a factor that greatly depends on the mirror. And as also note, the mirror should be front/top coated, not your standard bathroom mirror material where the coating is behind the glass. There are even some lightweight mylar mirror materials, but usually with greater light loss related. Also be aware that dust, scratches, smears, etc. on the mirror can show up in the image.

But perhaps the biggest potential problem is optics. Things are never quite in the field as they looked on paper and you mirror mount/frame needs to allow for quite a bit of flexibility and adjustment. There are several manufacturers who offer packaged single and double mirror vertical systems and over the years they have developed very flexible adjustment schemes. Your mirror system may not be that complex, but you may quite literally need to be able to do something like moving one corner of the mirror in or out. When using mirrors, plan on spending some time getting everything tweaked and set before fixing anything in place and then some more time to tweak even more after that.

Another consideration is double bounce. If the mirror is at 45 degrees or greater from the screen this should not be a a problem, but at shallow angles you can actually get light hitting the mirror, then the screen, then reflecting back to the mirror and back to the screen at another point.


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## LD4Life (Jan 21, 2008)

museav said:


> And as also note, the mirror should be front/top coated, not your standard bathroom mirror material where the coating is behind the glass.


Yeah, we are using top coated glass. Somebody mentioned that earlier and I took their advice.


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## codered11343 (Jun 27, 2008)

I would have never thought of this, but its such a good idea, and very obvious once I head it. I have been looking for a way to enlarge a projection that I will be doing in a few weeks and this may have saved me.
Thanks! This is why I love this forum.


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## LD4Life (Jun 30, 2008)

If you want any more information including pictures of my setup, just email me and I will reply with whatever info you would like.


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## Schniapereli (Jul 6, 2008)

I have actually worked with a projector with a built in mirror. The mirror had a strange curve where it was like a convex U at the bottom but towards the top it would get flatter. We could project an image maybe 7 feet wide from 4 feet back, but the projection was very high from the projector. We ended up hanging it upside down and flipping the image because the screen was closer to the ground.

I am not sure what brand it was, but it was fairly interesting. I wouldn't consider it to be professional quality for a very large screen, but I thought the mirror part might be interesting.


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## ruinexplorer (Jul 9, 2008)

Schniapereli said:


> I have actually worked with a projector with a built in mirror. The mirror had a strange curve where it was like a convex U at the bottom but towards the top it would get flatter. We could project an image maybe 7 feet wide from 4 feet back, but the projection was very high from the projector. We ended up hanging it upside down and flipping the image because the screen was closer to the ground.
> 
> I am not sure what brand it was, but it was fairly interesting. I wouldn't consider it to be professional quality for a very large screen, but I thought the mirror part might be interesting.



Sanyo makes a cool LCD projector like this. However, the resolution is a low 1024 x 768.
SANYO LCD Projector Homepage | Lineup | PLC-XL50 Features


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## museav (Jul 10, 2008)

1024x768 is actually probably the most common resolution for cost effective projectors, it's only low res if you have true high res sources.

Be careful with the short throw projectors like that Sanyo or the NEC WT610E, they can be very useful but they have no optical zoom, image shift, etc., so they have to be a a very specific location relative to the screen both vertically and horizontally in order to get a specific image size. In addition, they are relatively low output (2,000 lumens for both models noted) and limited in the image size recommended (60"-80" diagonal for the Sanyo and 40"-100" diagonal for the NEC). So a great solution for some applications but rather limited in the range of proper applications.

I think the best demo of short throw I saw was the NEC WT model combined with a dual bounce mirror system that was shown at InfoComm a year or two ago and that resulted in a 100" image in about 3' of depth.


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## ruinexplorer (Jul 10, 2008)

museav said:


> 1024x768 is actually probably the most common resolution for cost effective projectors, it's only low res if you have true high res sources.
> 
> I think the best demo of short throw I saw was the NEC WT model combined with a dual bounce mirror system that was shown at InfoComm a year or two ago and that resulted in a 100" image in about 3' of depth.



No doubt that 1024x768 is common, but it is becoming more of a rarity that your source will be that low of a resolution. I don't understand why Sanyo insists on staying with that resolution when competitors like Canon keep more in line of 1400x1050.

At Infocomm this year there was a similar double bounce at a couple of booths. My memory could be off, but I think they exceeded the 100" image. Then again that wasn't what I was going for. But there definitely were some nice presentations (even onto plexi).


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## LD4Life (Jul 15, 2008)

Just to give you a reference as to what we were doing. Our final image was 32' wide by 12' tall. This was single bounce off of top-coated glass. I'd have to look up the measurements of the mirror. But, yeah, that's what we did.


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## cwin26 (Sep 2, 2008)

Hey I am a student at Viterbo University in La Crosse Wi., we are doing a production of Our Town and we want to do rear projection but we only have about 13-15 feet of throw distance and we need to project on a screen 30'x25'. Could I get your formulas and as much information as you can provide me about how you achieved your enlargement?


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## ruinexplorer (Sep 3, 2008)

We would need the specs on your projector and lens to be of much help to you.


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## SHARYNF (Sep 3, 2008)

when you use a mirror system to fold the projection space you do not reduce the light path, you "fold it" so if you take you projector and move it back to the distance where you get the size image you want and measure this, you then have the total length of the light path, and you can then look at using mirrors to fold it. If you want to know the size of the mirror you need (again not by calcualtion but by trial) you can then place something to project on at the point of the mirror, the size of the image on projected temporary surface will be the size of the mirror needed.

Here is a pdf which goes into more detail

http://www.fordav.com/publications/cb16.pdf

Da lite will calculate it all for you if you want based on projector lens etc but the pdf above give you the theory of how it all works

Sharyn


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## museav (Sep 3, 2008)

Also remember that you can 'fold' the light path horizontally or vertically depending on whether you have available height or width. And be careful of folding it too much, if the mirror gets shallower than 45 degrees to the screen then you may have to start looking at whether secondary reflections (i.e. reflections off the screen and back to the mirror) start to end up potentially reflecting off the mirror again and hitting back on the screen.


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## SHARYNF (Sep 3, 2008)

Brad is correct you can fold vertically or Horizontally , Usually with home stype projectors you go with vertical since the keystone correction that you tyipcally use to adjust things only works in the vertical.

Sharyn


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## sk8rsdad (Sep 3, 2008)

You might want to check out Johnny Lee's video on Youtube about hacking a Wii remote to automatically image correct a projector to a screen. 

In one of his other videos, he has the images conforming to various foldable displays like umbrellas, scrolls, etc. He claims that he can accurately render from as little as 2 degrees from the plane of the screen, and can converge multiple projectors from many angles to minimize shadows. 

The possibilities for theatre applications are intriguing.

I believe the software is available for free from his website.


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## SHARYNF (Sep 4, 2008)

If I read his info correctly there are several distinct projects, and the projector calibration one which is very exciting, is not related to the Wii remote project. The Projector calibration uses an optical sensor pad with a usb connection to a computer software program that is altering the graphic image. I could not find any link for building the sensor pad or the software.

The wii software was more as using the remote as a position sensor for objects.

Again this is how I read it, interesting if someone can find more information
Sharyn


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## museav (Sep 4, 2008)

On the automatic image calibration video, look carefully at the very beginning, my understanding is that this is work undertaken with the involvement of a manufacturer, in this case Mitsubishi. Many such projects are not undertaken just for fun nor just for advancing the art, they are focused research underwritten by manufacturers looking to develop new products or technology. In other words, you may soon be seeing much of the technology shown in these but it will likely be in specific manufacturers' products.


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