thank you for your reply, I am asking because i've heard that kenko is much better (1,4x) than canon and I am planning to buy one.I now own one tamron 2x but I think is an older version ,I don't like it .it does not work with the 100-400 even in good light (I understand why) and the only way to take a picture is using the live view and MF but the results are bad,real bad.so canon it is then,thank you again