Short-Throw Projectors

Numerous classrooms have been outfitted with a screen, whiteboard and projector. However, this ubiquitous setup has two problems:

  1. If you stand in front of the screen while teaching you get a punishing shot of projector light in the eyes and you promise yourself not to do that again.
  2. If you want to use both the projector and the whiteboard you are constantly running the screen up and down.

We recently remodeled one of our classrooms and solved both problems as well as gaining some new capability.

Short-Throw Projectors

The first technology is the short-throw projector. One of the parameters for selecting a projector is its throw ratio. The throw ratio is the distance from the projector lens to the screen divided by the width of the projected image. For most classroom installations the throw ratio is somewhere between 1.8 and 3. This would mean that the projector is 2-3 times as far away from the screen as the screen is wide. On many projectors this throw ratio can be modified by means of a zoom lens.

Short-throw projectors generally have throw ratios of less than 1. Some even have throw ratios of 0.5 which means the image is twice as wide as the distance to the projector. Images 9 feet wide can be produced by a projector just a few feet from the screen. The key advantage of a short throw projector is shown in figure 1. Note that where the standard long-throw projector shines in the teacher’s eyes and casts a shadow, the short-throw optics project behind the teacher. The teacher is now free to move about in front of the image.

Figure 1 – Short throw projector without shadow

There are a variety of vendors that sell short-throw projectors. Our first one was from NEC. We have recently installed several models from Epson and I have also seen a nice model from Mitsubishi. A web search for “short throw projector” will generate several hits at many price ranges.

There is one caveat. Short-throw projectors at the economical end of the price spectrum tend to have a maximum image size of 100″. This is great for a class of about 30 but gets a little small for larger classes. For our purposes we needed more expensive models to get images of 200″. This is less of a problem for large auditoriums because the speaker is so small relative to the screen size the the projection for a long-throw installation is almost always over their head.In a really big classroom, the short-throw projectors do not offer much of an advantage.

Projecting onto whiteboards

Our second problem was running the screen up and down when moving between the projector and the whiteboard. This is very frustrating. The solution is from Walltalkers. They sell whiteboard material that is applied like wallpaper. You install this from chalk-tray level up to the ceiling, creating a full-wall whiteboard. We then project directly onto that whiteboard surface rather than a screen.

This has the delightful property of being able to write directly on the projected image with a whiteboard pen. This has added a lot of interactivity to my lectures and lets me clarify points much better than trying to draw on PowerPoint slides with a touch pad. To convert the whole setup from a projector screen to a whiteboard, you simply add a black slide. The whiteboard now behaves like a normal whiteboard. When this material is used in combination with the short-throw projector you are able to move freely in front of your material while drawing on top of it, all without projector eye pain.

A traditional problem with projecting onto whiteboards rather than the normal screen is the hot glare spot that appears right in the middle of your projected image. This is solved in two ways. First, the Walltalkers material is not as shiny as traditional whiteboards. It is more diffuse and thus has less glare. The second solution comes from the short-throw projector, as shown in figure 2. With the long-throw projector, the angle of reflection goes right back into the student’s eyes. With the short-throw that same reflection falls harmlessly on the floor.

Figure 2 – Short-throw glare into the floor

Figure 3 – Classroom installation of short-throw projectors and whiteboard

Installed in a classroom

Using these ideas we remodeled a 60 student classroom as shown in figure 3. Note that the entire front wall is covered with the Walltalkers material, (plus a nice oak boarder added by our carpenter shop). We have installed two Epson short-throw projectors. Together these projectors cover the entire front wall with pixels.This full coverage would not be feasible with standard projectors because the instructor would have no place to hide from projector blindness. With the short-throw projectors the issue never comes up.

To use these two projectors we installed LearnSpace software from Pixelture on the computer in the podium. This software allows us to wirelessly project multiple windows from my laptop onto the wall. I can also have students share their work from their laptops as well. If I am doing a PowerPoint presentation, I can simply copy slides onto the other projector to keep a context or problem for the student’s benefit while the rest of the slide deck moves forward. This is much more powerful and flexible than simply cloning my screen to a single projector.

This has turned out to be a lovely teaching environment. I hope you get to create one of your own.


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