Rembrant-

I've done Orchid macros with a 5x7 - my intended goal is platinum contact prints. I use a Nikon 120 Apo-Makro lens which fully covers 5x7 at infinity, and has plenty of depth of field even at close range. I did this work in the field (well, the Rawlings Conservatory up in Baltimore), using a lightweight Manfrotto carbon-fiber tripod, and had no issues with the tripod getting in the way. I'd much rather have the big ground glass to work on, especially when shooting macro work, so I can actually see what I'm focusing on.