Ive googled like crazy and cant find an absolute answer. I found a kenko compatibility pdf form http://www.kenkoglobal.com/pdf/TELEP...bilityList.pdf , and has a warning that kenko tel could stuff up the camera or lens if put on the wrong/ non adaptable lens( tammy or siggy). But I have come across posts with people using it with other siggys just not the 105 macro siggy. I have come across one post with someone saying it stuffed up 2 of his cameras ( focusing issues I think ).
reason Im looking at the Kenko is that it will fit my (future) Nikon 70-200 f4 as well.