Digital Projection in Sanctuaries: The Throw Ratio Problem

Low-cost digital projectors are available for as little as $400. However, in the price range of $400 to $2000, the throw ratio is very seldom other than 1.9 to 2.1. For projecting from the back of a 30 foot room, this would require a screen 15 feet wide. On the other hand, a large but practicable screen is at most about 10 feet wide. To accomodate such a screen, a throw ratio of 3 is required. The price tag on the projector suddenly jumps up to near $20,000. Alternatively, the projector with a throw ratio of 2 could be placed 20 feet back from the 10 foot screen. This works out well in schools where ceiling mounting is possible. But, in a sanctuary, ceiling mounting may not be possible because the ceiling is too high, there is no way to route the cables or that the cables would be simply too long to allow good video. Putting the projector on the floor means putting it in the aisle introducing another set of problems including the possibility of tripping members with the cables. Temple Beth El put time and effort into the possibility of designing an auxilliary lens that would increase the throw ratio from 2 to 3. A combination of ray tracing and mounting a projector on an optical bench testing different arrangements of lens elements was tried. While lens designs similar to the add-on telephoto lenses sometimes used with small cameras could increase the throw ratio, the needed ratio of 3 could not be achieved.

There are two barriers to increasing the throw ratio from 2 to 3 with an auxilliary lens. (1) Any such lens necessarily increases the f/-number of the system making the image so dim that it is unpleasant to view when the source is 1000-2000 lumens, and (2) aberrations become extremely difficult to correct as a throw ratio of 3 is approached. However, by the same token, an ultra short throw ratio would produce a gain in brightness for the same number of lumens.
On investigation a projector with a throw ratio of less than 0.5 turned out to be available. Sold by 3M the Vikuiti Model 710 DLP projector sold for $1,699. While this is not cheap, it costs less than a personal injury lawsuit. Temple Beth El purchased this projector and uses it as shown. It sits on a stand a little over three feet from the screen, well away from any foot traffic. It has worked excellently for a lecture series held in the sanctuary. The projector, stand and screen are easily removed for religious services. Sadly, this product was being withdrawn from the market when Temple Beth El ordered it. The Temple was among the last to receive one. However, the technology exists and similar units are available. One just has to look for them.