Okay now you all have confused the crud out of me. . .if you put a tube on a lens how can the focal length possibly get larger??? My 760mm lens is wide and shallow whereas my 150mm lens with appropriate cone mount is decided similar to mounting a lens on a tube and the focal length is less. Doesn't focal length mean the greatest possible diagonal which the lens can handle?
Same thing with bellows extensions adjustments. The longer the bellows are extended the larger the aperature needs to be wherein f8 would become f5.6, not the other way around.