Graham, I use an Ebony SW45 which is great for wide angle photography but will only allow infinity focusing of lenses to 180 or a little longer if they're of the tele-photo design. I do use lenses up to 240 with the 'top hat' panel and extension tubes. An extension back is also available for using longer focal length lenses. But this of course all adds to the cost.
What I like about the SW it's of the non-folding design so will accept almost any lens attached when transporting. This design is compact and quick to set up, useful for those fleeting moments The bellows are also very supple and allows great flexibility with short focus lenses like the Super Angulon 47XL and the Apo Gradagon 35 (this lens will cover 6x12cm but not 4x5).