I've got a few lenses for my camera: a mid-50's 5cm Elmar Red Scale, a 1934 9cm Elmar and the latest addition, the 1937 13.5cm Hektor.It's taken me a couple of years to get these lenses, and I'm now saving for either a 3.5cm Elmar, or one of the Telyt lenses to fit the Visoflex I. Anyway, that's for much later! Right now, I seem to be favouring the uncoated 9cm lens for macro work, set to f22.
Both the 9cm and 13.5cm lens can be unscrewed from the main focusing body, leaving you with just the lens assembly complete with diaphragm; on the 9cm this gives you from f4 through to f36, with the Hektor 13.5cm your choices are pretty similar - from f4.5 through to f36.
I've yet to use the 5cm on the bellows, though it will fit using the same adapter as the 9cm lens head (the 16558 adapter ring). This adapter converts the large thread at the end of the bellows to an L39 screw thread.
If there's one area which is completely confusing within the world of Leica macro, it's which adapter is needed for which lens, based on which Visoflex. Quite frankly, it's a nightmare and there's plenty of conflicting 'advice' out there on the Internet!
As if to prove the point, having bought the Hektor lens, I wanted the adapter to fit the 13.5cm head on to the bellows. Searching the Internet just left me more confused than when I started, and it seems that originally the bellows would have been sold with adapters - including a 2-part adapter allowing the user to make this fitment. The confusion is made worse by the Visoflex reflex housing - the early PLOOT and Visoflex 1 housing are different depth to the later Viso II and III to allow for the differences between the screw thread cameras and the M bodies, I believe.
I found an adapter tube - a Leitz 16472 - that allowed the 13.5cm head to fit the 16558 adapter I already owned, from Ffordes (very good service, and they come recommended. http://www.ffordes.com/). However, with this setup, it's only good for macro work, which is after all why I bought it; but, the correct adapter should still allow you to focus to infinity and this one doesn't. I'm guessing that it's actually for the Viso III? The very fact that it's got a number rather than the old Leica 5 letter code, must mean that it was made after about 1960 anyway.
In summary then... don't overlook the old uncoated lenses (or rather, do overlook them, so that I don't have to save up as much money to buy them!). They still deliver the goods and without the high contrast of modern lenses, they have a colour rendition all of their own.
The adapters - confusion reigns! I would suggest that if you are tempted to purchase a Visoflex and bellows, that you get one that comes with some adapters as it would be hugely frustrating to have the main gear sitting there, but being unable to use it due to not having the right adapter! The 16558 should be considered the main one to get hold of as it allows you to fit any L39 screw thread lens.