Just received the new Canon 100mm 2.8L Macro IS lens. With my 1Ds MKII, the focus on my copy is fast and accurate. However when paired with either a Kenko 300 pro 1.4 tele or a tamron 1.4 tele the autofocus has huge problems locking on. It nearly continuously flutters making these pairings completely useless! Auto servo or single shot settings does nothing to improve the autofocus lock. Neither does changing the focus setting to a single point. Most likely the Kenko and tamron tele's will require an update in order to function properly with this particular lens. As many readers will know, both of these tele's work very well with the original 100mm 2.8 macro.
I leave for Fiji on Saturday where I plan on using the new lens. However I will use diopters (internal and external) for close up work. I will try and post my impressions on the difference between this lens and the old version when I get back.
imasleeper