ShadowHillsPhoto wrote in post #18543357
To be fair though, your experience is all based on the older version 1 400 2.8, right? And maybe the older 2xII as well? The 2xIII converter paired with one of the Mark II primes is far from horrible. Especially on a 1DX or 1DXII.
Tom Reichner wrote in post #18543372
With the previous IS version (not the current IS mark 2).
With both the Canon v2 and v3 2x extenders - absolutely no difference whatsoever in either optical quality or in AF performance. I believe that the v3 only performs better when paired with the latest v2 supertelephotos.
Yes, the differences in AF performance are only noticeable with the V2 lenses , BUT to really get the best perfoamnce you also need the AF system found ONLY in the very latest bodies. (1Dx2 and 5D4)
All others, (yes even a 1Dx) you won't get the full benefit of the V2 lens / MarkIII T-con combo. Without the right body, the playing field is so different that we aren't talking about the same game.
ShadowHillsPhoto wrote in post #18543440
Yes, the 500mm. Of course I only had one copy of the 2xIII and one of the 2XII to try, so I can't rule out copy variation with the limited sample size. Even so, if you do a quick search for reviews of the 2xIII you'll find that I'm far from being the only person that has found the 2XIII to have an edge.
My results were less like yours and more like Tom's,. before I had a V2 500mm, I had both versions of the 2X and found them to be near identical when used with the Gen 1 IS 500mm and a less than state of the art body like the 5D3 or 1D4 or 7D2. No AF improvement, no IQ improvement. However, I was always quite happy with my MKII 2X T-con on the 500mm.