For your interest, the throw in my little venue at work here is 15.5 metres from projection room to screen, and our fancy new HD projector needed a lens upgrade for that. At 6000 lumens, and with the longer focal length, it projects a 2.5m x 4.44m (16:9) picture really brightly. The 16mm Kinoton here has a 45mm f/2 lens for the same throw with a 1.2kW lamp, and is also very bright.
It has been interesting looking at some of the fancy new projector installations in lecture theatres here - one I looked at yesterday had a 4 lamp DLP projector installed (ceiling mounted, really close to the screen), just to compete with the GIANT west-facing window running the length of one side of the space. Technology battles architecture...
new lecture theatre.JPG