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3-D Stereo

Supply List
Rear projection Screen Frame
Projector/Computer Cart
Projector stand
Filter Holder
Rear projection Screen
Front projection Screen
DLP projectors
Projector add-on module
Polarizing filters
Polarizing glasses
Computer
Flat panel monitor
Graphics Card
Links

3-D stereo relies on the concept of depth perception. Humans perceive depth by seeing an object from the viewpoint of each eye and then combining those two images into one. A 3-D stereo image relies on viewing one image with your left eye and a slightly different image with your right. They key is having a stereo pair, two images that were taken roughly 2 1/2 inches apart from one another, the approximate distance between your eyes. This tricks the brain when viewing a flat image to see it having depth. Viewing these images can be done in several different ways, such as with a View master or with special glasses.

Traditionally, red/blue, also known as anaglyph, glasses are thought of when viewing a 3-D stereo representation. The image has a duplicate red image slightly off of another blue image. The glasses filter out the red image in the red eye and the blue image out in the blue eye, ergo one image for the left and another for the right. The issue with anaglyph glasses is that the color of the images is a bit off, and is not an accurate portrayal of the object. That is where polarizing lenses come into the picture.

Polarized viewing of 3-D images is based on the same concept as all stereo images, forcing the mind to see one image with the left eye and another with their right. The lenses are used in conjunction with a two-projector system; there is one lens for the left eye and another for the right. In Linear polarization each lens filters light at a 45-degree angle, just in different directions. The glasses match the polarization and ensure that the image from the “left” projector is viewed by the left eye and vice versa for the right. The image is crisper and not as color distorted as when viewing with red/blue glasses.

Circular polarizers take linear polarization a step further. In linear polarization, the minute the glasses are no longer at a 45-degree angle, such as when someone tilts their head, the image loses its 3-D effect. Circular polarizers filter light in a spiral pattern, clockwise for your right eye and counter-clockwise for your left. No matter how the filters or glasses are rotated the image can still be seen in stereo.

3-D stereo images can be used for a multitude of educational uses. They can be utilized in conjunction with topographic maps to help students in interpretation of heights. They can help students visualize the size and scale of molecules. In a 3-D movie format they could help teach the concept of movement and velocity in physics. 3-D stereo systems, such as the polarized filter system previously discussed, are significantly coming down in price and are now becoming affordable for educators.
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Rear projection Screen Frame

http://www.bertelkamp.com/
We constructed our own frame for the rear projection screen. It provided us with more flexibility and portability. Although the manufacturer does not recommend rolling or folding the screen on a regular basis, given our building constraints it was a more viable solution.

In designing the frame we took a page out of Purdue’s book and went with the 80/20 catalog of products. Using Bertelkamp (an 80/20 distributor) we were able to send dimensions to them and receive CAD drawings. Our biggest challenge was ensuring the screen would fit correctly. The frame is vertically mobile in case the room warrants a lower or higher screen. 80/20 is an adult erector set of sorts made of extruded aluminum, the lengths of which can be custom cut to suit your needs. They have a series of brackets and fasteners that fit into grooves and bored holes to hold the bars together.

Download PDF of frame schematic

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Putting the screen together

Putting the screen together requires at least two people and attaching the screen requires three. You’ll need a big area to spread everything out. It is important to work from the inside out. If you forget to place a piece on the inside grooves you may have to take the entire project apart to get to it. We happened to be using a snap screen and it was important that the t-nuts be fed into the grooves before we attached the frame together.
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Projector/Computer Cart

http://www.bertelkamp.com/
We constructed our own computer cart for this project as well. The same 80/20 products were used for the frame construction, just on a smaller scale. The computer itself fits on the bottom rack with the keyboard, mouse, flat screen monitor, and projector stacker on the top. The projector stacker can be removed from the cart for rear-projection or kept on the cart for front-projection.

Download PDF of cart schematic
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Projector stand

Chief Registration Stand RSH-1B
http://www.bhphotovideo.com
We used a typical projector stacker, but did not purchase an addition tray. We had found that keeping one projector stationary and then maneuvering the other projector to “fit” the first projector worked well for us. The biggest issue with stacking projectors is that the projector on the bottom gets quite hot – having a fan to disperse the hot air is necessary.
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Filter holder

http://www.bertelkamp.com/
We custom made a filter holder for our projector stacker. We used the 80/20 extruded aluminum product again, but on a much smaller scale. It allows for a variety of height adjustments and we were able to attach it directly to the projector stacker. If using plastic filters do not place the filter holder very close to the projector or for long periods of time. They have a tendency to melt.

Download PDF of filter holder schematic
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Rear-projection screen

Disney Black 72”x96” snapper screen
http://www.tierneybros.com
A rear projection screen allows for the projectors to be behind the screen so that viewers can get as close to the screen as possible without blocking the image. When rear projecting you will need a room that has a good deal of space behind the screen to place the projectors. It also helps to place the projectors on the floor. If you plan on making your own frame it is important that you also ask for the female snaps (snaps only – you can buy the bolts at a hardware store) to match the male attached to the screen.

  
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Front-projection Screen

Dalite Picture King 72"x96" Silver Matte
http://www.bhphotovideo.com
When projecting 3-D stereo images using polarizing filters it is important to use a screen that preserves polarization. Common white projection screens will not work; a silver matte screen is required.

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Projectors

inFocus LP530 DLP
inFocus HW-ECM enhanced connectivity module
http://www.cdw.com
When filtering the light from the projectors with the polarizers a good deal of brightness is lost. It is important to purchase a high lumens projector. If you plan on rear projecting ensure that a rear projecting function is available. The enhanced connectivity module is primarily for the Monitor out, that enables what is being projected to also be seen on the monitor (great when you don’t want your audience to see your preparation).
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Glasses

Metal Aviation Circular Polarized Glasses
Plastic Linear Polarized Glasses – Theme park style
http://www.berezin.com
We have a variety of different glasses for demonstrating 3-D stereo. For linear polarization we used the traditional theme park style glasses. Circular polarizing glasses do not come in a wide variety of styles and are more expensive than the linear ones.

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Filters

Circular 5x5 Projector polarizers
Linear 4x4 Projector polarizers
http://www.berezin.com
It is important when setting up a linear polarized filter system that you have the appropriate filter in the correct position. To test this, place your glasses on and close your right eye, the right projector filter should be black, repeat with the left eye. If the filters do not appear black (i.e. all of the light is blocked) rotate or flip the filter.

  
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Computer

Dell Dimension
nVidea Quadro4 750 XGL
http://www.dell.com
The most important piece of the computer is the video card. It must be able to support a two monitor out system and have Open GL Stereo features.

  
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Helpful Links

http://geowall.geo.lsa.umich.edu/
http://resumbrae.com/info/cheapvr/polarize.html
http://www.berezin.com/3d/
http://www.pokescope.com/
http://www.evl.uic.edu/cavern/agave/docs/setup.htm
http://www.inms.umn.edu/convenings/wallsummit/JoyofWall.htm
http://astronomy.swin.edu.au/~pbourke/stereographics/

  
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