I really enjoy this lens. I have compared it to 100-400Ls (3 copies), and it outperformed 2 of the 3. What I have found is that the 100-400L MKI is better than the Sigma at 400mm, but the Sigma at 500mm is better than the Canon at 400mm.
Basically this lens:
- is sharper at 500mm than the Canon 100-400 at 400mm, so adding a 1.4x to the Canon isn't going to help matters any.
- is very heavy, but not too much more than the 100-400, nor is it much longer when extended.
- AF is quite fast, but not quite as responsive for the initial acquisition, but once it locks, AF seems to be about as fast as the 100-400L
- Stabilization is much better than the 100-400L
- Comes with a soft case, hood, and tripod ring, and a better warranty.
- Has a pseudo-macro mode at around 200mm or so, giving you a very short MFD to get more of a macro look.
- Having 50-500 is a great tool, but 50mm has mediocre IQ in my experiences
- Bokeh quality is better than the 100-400L, the Canon has a nervous bokeh when lots of details OOF
- Takes 2x pretty well if the pins are tapped, one of the samples below were used this way.
