as some of you may have read in earlier posts, i am currently saving money for a 100 f/2.8L macro lens (almost there), but i also want to pick up a 1.4x converter for my 70-200f/4. i have of course been eyeing the canon 1.4x......but what about 3rd party converters, i.e. sigma, tamron, kenko?? does anyone have experience with these converters, or perhaps know how they perform, besides the usual company propaganda??? info and advice is appreciated


jim