For ULF the only two true lenses currently being produced are the big buck Schneider XXLs one is 550mm and the other is 1100 if my memory is working correctly.

I only use 12x20, like Michael. I use a Fuji 600C, a Fuji 450mm CMW (not the little 450mm C), and a Schneider 355mm G-Claron. I am lusting for a 210mm Schneider Super Symmar XL which covers 12x20 and some say up to 16x20, also am after a 30 inch or 35 inch RD Artar.

Hope it helps.