Wow, we hit a nerve here. Far be it from me to be a defender of Sigma's AF -- I regularly harpoon the AF on the 35 and 50 Art lenses -- I think the 85mm Art is a different animal for the better. Hear me out.
First -- when we malign the rep of Sigma's AF, it's not about front or back focusing, so please stop bringing a USB Dock to a gunfight. Front or back focusing the dock can address, yes, but most people's beef with the Art lenses is
inconsistent focusing where trying to hit the same damn target (even on a tripod in controlled conditions in good light) can inexplicably whiff 1 or 2 times in 10 -- the dock can do nothing to address that short of delivering a new firmware update.
Calibration does not solve inconsistently hitting/missing the same target.
Second -- not all Art lenses are plagued by this inconsistency. I've personally experienced it on the 35 Art, and the 50 Art's problems are well documented by trusted reviewers.
But the 85 Art appears to have turned a corner. I do not know if this is due to the new additional power the focusing motor has or if they just worked out a bug with their EF communications routines. But the proof is in the pudding:
- http://www.lenstip.com/491.10-Lens_review-Sigma_A_85_mm_f_1.4_DG_HSM_Autofocus.html
In their general lab test, the miss rate was so low it was not reported. For perspective, the 35 Art had a 2.5% miss rate and the 50 Art had a 6-7% miss rate and exhibited a nutty AF stuttering/indecision problem on one of the test bodies. So one reviewer says the 85 Art is a very solid AF performer. Consider: the 85L II had a 3% miss rate in their testing.
LensTip even went a step further and ran a separate battery of more stringent tests and at f/1.4 the 85 Art only exhibited a 2% miss rate. That's actually a phenomenal result -- there are certainly some L lenses that would not hit that bar.
- Bryan Carnathan at TDP -- who rather famously nailed the 50 Art AF problem -- gave a much better review to the 85 Art:
"After capturing over 600 tripod-based images of various subjects strictly for the purpose of testing AF, each capture starting in an out-of-focus condition, I found that this lens focuses consistently accurately. Not every image is perfectly sharp, but a very considerable percentage of them are."
I am not saying the 85 Art is flawless. I am saying Sigma appears to have greatly diminished the Art lenses' biggest limitation. The reasons to avoid buying this particular lens are very small -- lack of IS, lack of sealing, it's too big, etc. -- but optically it is dynamite, the AF is significantly improved, and it's a value for the ages. And lest we forget, I'm no Sigma apologist. I've been one of their biggest critics on this issue. If I needed an 85, I'd get this one in a heartbeat.
- A