Can anyone suggest a decent 2X converter for use with the Nikon 28-200 2.8 (not the AF-S version, but the 2-ring tripod collar version)? I need autofocus capability at a reasonable price for only occasional use. I am thinking about the Sigma 2X APO and the Kenko AF 2X MC7. Any experience and recommendations on these or any other comparably price converters would be appreciated.
