I would like to be able to calculate how much bellows extension that I would need for a given focal distance. As in knowing the lens size, how much bellows would it take to focus at two feet ? Is it possible to calculate the image size as well ? 1:1, 1:4, etc ? I have three lenses in my arsenal - A 210mm Caltar S II, A 300mm W Nikkor and A 165mm Schneider Super Angulon. I have a Cambo 8x10 legend and a Cambo 4x5 legend. Using the pieces parts from each I have just about four feet of bellows. The rails from each screw together and I can use the front standard from my 4x5 and couple the two bellows together. I would like to do some close up work with my 8x10 and would rather plan ahead than use trial and error given my limited amount of experience in the studio. Up to this point I've been a landscape guy. Any help, advice, or opinions would be most appreciated.