« on: August 05, 2012, 12:27:54 PM »
I shoot with a 5D3, have not tested how many stops the IS is useable, but don't think the TC itself affects IS other than the increased focal length. AF is noticeable slower with the combo 300 version 1 and 2x II, so The challenge for BIF is focus more than hold ability. Dropping to the 1.4x solves the focus issue and since you are experienced with tracking BIF with the 100-400, I think you will be amazed at the quality of the 300 v2 plus 1.4x III. When I have a chance I will post some BIF photos with either the 1.4x or 2x.