jbrackjr wrote in post #16531402
^^Well if you said a 400 with TC I would agree. The 100-400 is a great lens, but with a TC it's pretty bad.
Pretty bad at what? AF may be compromised, but a good copy of the 100-400 should be fairly pixel-sharp with a 1.4x. When things all come together, I get fairly pixel-sharp results with the 100-400 and the 2xIII on my 6D.
I shoot my 100-400 at 800mm with the 2xIII all the time. I can't see any visible loss of global contrast, and there's always more detail than with cropping, unless I have to rely on AF for a BIF or such, in which case a pixelated bird is better than one with a lot of pixels, but out of focus.
If that is all the Tamron could do at 600 I think most people would be disappointed.
There's one plus that's a given, though. More subject light, due to the larger aperture, and therefore, less noise. The Tamron, wide open, gathers almost a stop more subject photons than a 400/5.6.
I would take the Canon ps super zoom over using a TC on my 100-400.
I feel very compromised when using my SX50 compared to my 100-400 with a 2x.