In their AVS Special Guest thread, Don Stewart et al say that the Grayhawk is designed for projectors that put at least 11-12 foot lamberts on the screen. He also did a calculation for Lance, where he said that a Davis 450, with spec'd 500 lumens, would theoretically put 13.5 ftl (is that a real abbreviation?) on an 80" x 60" Grayhawk screen. He said realistically, you'd probably get about 10.
Now, I'm thinking about using a Davis DLX650 clone, which is rated at 800 lumens, on a 100" diag (89" x 48") 1.85:1 screen. I'm also considering using an anamorphic lens, vs. not using one. If I use an ISCO, I'll be using all 768 vertical pixels, whereas if I don't, I'll be using about 554 pixels, or 72%. So without the ISCO, I imagine I'll have 72% of the foot lamberts I would have *with* an anamorphic lens.
So now I'll try to get myself in trouble by scaling the 10 foot lambert number that Don quoted. If I take 800 lumens / 500 lumens * 72% * 10 foot lamberts, I get 11.5 foot lamberts. But I don't think that takes into account my wider screen... Do I adjust based on the linear width of the screen, or the increased area, or what? Or am I hopelessly lost? I'm sure it's the latter...