Projector Modifications
Updated March 8, 2009
In order to construct a projecting multi-touch display, a projector that can focus at the appropriate distance and produce an appropriate image size is required. The obvious solution, purchasing a projector of the type known as "short throw" is attractive, however, the price makes it unreasonable, especially to dedicate the projector to the project. Instead, I am using a donated projector from St. Norbert IT and Tech Support departments: a very large, and rather old, InFocus LitePro 570. The specs on the projector provide that, with a 5.7 foot throw distance (the distance between projector and screen), a 5 foot diagonal image is produced. However, there are two problems with this: I am building a screen that is smaller than 5 feet, and it would be cumbersome to say the least to accommodate a 5.7 foot throw distance.
Since we are the rear projecting the display, the special features of a short throw projector that make it useful for front protection are not required. Therefore, we simply need to be able to focus our LitePro projector at a shorter distance to produce a smaller screen size. The focus knob stops when turned externally, however, on a hunch, I disassembled the projector, hoping to be able to remove this focus knobs stop. I was successful, and was able to make the projector focus at a throw distance of only 33 inches, which would correspond a screen size of 29 inches diagonal. As a bonus, after disassembly, cleaning, and reassembly, the projector appears to be working better than before, and hopefully the image problems that plagued the projector previously have been solved. I documented this procedure with my camera.
Click on any photo for a larger version.
 Projector with cover removed |
 Image generating area: lighting mirror, light diffuser fresnel, panel, and projection fresnel lens |
 This screw keeps the lens from being turned past a point |
 However, it can be loosened and the lens can unscrew all the way |
 I put the lens back on but left the screw looser so that it could be focused closer |