I bought the 2.0 Version III extender to add utility to my 500mm f/4 L. I wasnt interested in doubling my 70-200mm as I already have a 100-400mm. My interests were: doubling the focal length of the 500mm f/4 for use on a 7D Mark 2 body to get maximum reach for long range shots, and on a 5D Mark 3...