Short throw projectors have a lot of advantages for classrooms and conference rooms:
- The short image throw allows for presenters to approach the screen without interfering with the image or having to look into the projection light.
- The short image throw also allows for several projectors to be placed in a small room, making it ideal for videoconferencing, or I-TV, classrooms
However, the installation of these projectors can be complicated. A small change makes a big difference in the projected image with a short-throw projector. I learned a few lessons installing a couple of Sanyo PDG-DWL100 projectors in a classroom. The problem was that with the size of the image that we were trying to project, we didn’t have enough height to project on the screen without having to tilt the projector which resulted in a keystoning effect that had to be corrected. However, when corrected, the image size was reduced: so you would have to back the projector farther from the screen, tilt it even more and reduce the image size again. I found that we were simply caught in a situation where we could not ever get the image we wanted without either lowering the screen or getting the projector higher than the current ceiling. You can see the issue with the photo below.
Here is the illustration of the projected image from the manual and you can see that this projector will always take 15% of the overall distance of the image from the screen before the image will start. This is more severe than some other short-throw projectors.
In this case I built a custom box that fit into the 2×2 ceiling grid so that we can mount the projector flush with the ceiling grid; a little to the left in the image below. We could attempt to mount the projector flush with the ceiling, but without some room for adjustment, it would be problematic at best.
With 20/20 hindsight, I should have used a smaller screen in this installation (which was the original spec, but we decided to use a larger size since it was being used for the instructor monitor in a videoconferencing classroom).