Occasionally I use a Mutar III along with the VS 80-200. Before I bought the Mutar, I contacted Carl Zeiss in Oberkochen, Germany, to know if there would be any major optical or mechanical drawbacks resulting from this combination. I talked at the time to Kornelius Fleischer, who told me that they recently had performed some tests of these two optics together which turned out amazingly well, although the Mutar III had originally not been designed for use with the Zoom.
I bought the Mutar and just can confirm his statement. If used on a tripod and stopped down to f 8, the picture quality is still within the range of what other Zeiss optics are delivering.