I have a 300 f/4 IS and was shooting with the 1.4x II on a 5D at Road Atlanta the other weekend. When doing some post processing in PS I noticed the max. aperture was f/5.7 not f/5.6. the shot was f/10, ISO 125. The 5D auto focus, as you know is f/5.6 max. I did not see a problem with auto focus, but I do not care much for the 1.4x II on this lens, camera combination. Without the 1.4x II the max. apeture is f/4 where it should be. Have not tried this combo on the 30D yet, but interested if any one elese has seen this, or does this lens need to go back to Canon for some fine tuning? Very sharpwithout the 1.4x. Have not had this glass but a couple of weeks.


JeffersonPoster