« on: July 01, 2013, 04:21:48 PM »
I have read that autofocus speed decreases by 50% with EF1.4X III and by 75% with EF2X III.I just got 500 II, paid a lot and if the difference is so small as negligible I prefer to not spend more money for now (I have version II teleconverters).
If you only shoot the moon and other things which move slowly or not at all, there's not a substantial benefit to upgrading. But if your subjects move, the improved autofocus performance with the MkIII extenders is reason to upgrade, if not for the IQ benefit.
Are there any measurements with version II ?