Which is the fastest focusing canon or third party lens in the 50mm - 100mm range?

Apart from the 70-200/2.8 II (which is quick) and sharp wide open, you might also think of the SIgma 50/1.4.

Provided it is MFA is set up to suit the aperture you're using, it works really well. Of course, things get weird when you change aperture causing focus shift to kick in. The reviews have the corners looking soft but I strongly suspect this is a result of focus curvature. It gives sharp images from about f/2.

Have you looked at the Sigma 50-150mm f/2.8 OS? I can't comment on AF speed but, it seems like it might be a good fit.

MATT0404 wrote in post #14817630
Have you looked at the Sigma 50-150mm f/2.8 OS? I can't comment on AF speed but, it seems like it might be a good fit.

This is only for crop camera's not the OP's 5Diii

EF 50mm f/1.8 II
super fast

moltengold wrote in post #14817921
EF 50mm f/1.8 II
super fast

if some one says nifty fifty is fast AF then they haven't shot with any other glass besides kit lens.

The 85f1.8 is very fast. I don't have any way to precisely compare relative speed, but the 24-105L is also pretty quick and accurate.

artyH wrote in post #14818140
The 85f1.8 is very fast.

+1 to that. I've not used 70-200 f2.8 IS II, so cant comment on it.