Nikon's 70-180 did 1:1.3(just looked it up again, and I originally thought it did 1:2 and you added tubes, but I got it confused with another lens I've had my eye on at the same time).

1:1.3 isn't too far off the mark I guess, and is a lot closer to the usual maximal marketing guff spewed out by Sigma and Tamron on some of their zooms!(1:3)

Two aspects of this lens that attracted me too it: Aperture is not variable over the focused distance(as a lot of macro lenses will be prone too. That is, if you set your aperture to f/5.6 at 180mm, it doesn't surreptitiously develop tunnel vision and in reality become an f/8 180mm lens. Most macro lenses do this, so you set your aperture and it stays there. As an example of how other lenses do this.. Nikon's 105VR Micro is an f/2.8 lens at moist focused distances, but once you focus down to 3m, it then closes itself down to f/3, and so by the time you've focused down to it's MFD(and 1:1) it's really an f/4.8 lens.
I guess that with a variable aperture design anyhow, and in reality quite a slow one at that (being f/5.6) this should be the case anyhow!
The second aspect of this lenses ability that looks attractive is the MTF graph. I've never seen any other lens produce this type of MTF graph, but the contrast measured is better at the long end of the zoom scale, than it is at the shorter end.

Look at any manufacturers zoom lens MTF data, and you always see them produce better MTF figures at the shorter end than at the longer end.

(for those that want to know, the MTF figure is also taken as a lenses ability to resolve detail.. ie. sharpness).

I remember Vanbar having one for sale not that long ago, for the princely sum of $1800, and this is long after the production of the lens was discontinued.