Not sure how helpful this is but I seem to recall that the light from a projector falls off at a rate equal to the inverse of the square of the distance. In other words it's not a linear reduction.
So a projector optimised for use in a room at (say) 5m distance is going to look pretty dim even at 10m and probably hardly viewable at 30m. Maybe check that out first.
Second is that boosting the light output is problematic because the heat will likely destroy the transparency, if not the projector. Standard cooling fans might not cut it.
The longer lenses you're noting were made so that conventional 35mm slide projectors could fill a standard screen in a larger hall or venue. There were also zoom lenses made.
I think you'd suffer less frustration by hiring a powerful digital projector from a specialist audio visual supplier. Kayell might be a useful point of enquiry.
I don't think the subtlety of film grain is going to be apparent when projected on the side of a large concrete building!
Last edited by Leigh Youdale; 08-16-2010 at 01:43 AM. Click to view previous post history.