I just fininshed watching a new youtube clip that pits the D4 against the 1DX and it clearly show the 1DX out performing the D4. What I did notice though is that the presenter fitted the D4 with an 85mm f1.4. I have that lens along with the 50mm f1.4 and the 105 f2.8. My experience is that the Nikon primes, except for the super teles, are slow focusing relative to the three 2.8 zooms. Whenever I use the 70-200 it is lightening fact and accurate, same for the 14-24 and 24-70.
It seems that most reviews are often with prime lenses. Using one of the 2.8 zooms might yield a different outcome when comparing brands, especially considering Canon primes tend to focus faster.
What has your experience been?
