p.2 #2 · 2X Extender III with the Canon 70-200 f/2.8 II
This just in...
I did the same test with the 5DM3 this afternoon. There are some differences. This is logical since a Full-Frame sensor will test a lens out it its edges.
All three lenses are very close when viewing the center part of the lens but the corners do reveal differences...
The sharpest all the way out to the corners is the 400mm f/5.6. The 100-400mm is very, very close to the 400 prime but CA is noticeable in the corners. In last place is the 70-200 f/2.8 + 2x TC. The corners are noticeably not as sharp.
p.2 #3 · 2X Extender III with the Canon 70-200 f/2.8 II
I think it's a very good combination for those times when I'm not going to have the 500 with me.
This one was taken hand held, from the top of a tiny boat bobbing on fairly rough water, in very poor light (ISO 1600 with a 7D; 1/1000 sec), wide open (f/5.6) from far enough away that the bird could not be see by most people on the boat with naked eye.
