Below I share ten 100% crops from one of the more-formal focus tests I performed. The subject is a large book properly aligned with the camera at a relatively close focus distance. Starting with a slightly defocused lens, each shot was autofocused using the center AF point that was very comfortably and completely covered by the book. The first 5 and last 5 images from this particular test are presented below and are representative of the larger test group. … The camera was a tripod-mounted EOS 5D Mark III with mirror lockup and the 2-sec self-timer in use.
Of those 10 shots, 4 are sufficiently OOF as to be unusable (3, 4, 6, 10). A 60% hit rate with a static subject and a tripod-mounted camera, particularly one with an excellent AF system, does not inspire confidence.
Also, this is a departure from the norm for Bryan's lens tests (and one, frankly, with which I'm not too pleased):
My evaluation lens was a short term loan from Sigma, as they offered the production-grade lens before it was commercially available.
Any time a manufacturer supplies a product to a well-known reviewer, a big unanswered question is whether the provided copy is truly representative of units purchased retail. Clearly, it would be in Sigma's best interest to pre-test a batch of them and pick the best copy they can find for review (in fact, they are supposed to generate measured MTFs for every lens they produce, so they have the data already).
I've always felt that one of the strengths of Bryan's reviews (in addition to their thoroughness and readability) is that he purchases review copies through standard retail channels (B&H may put him near the top of the preorder queue, but that's fine), and therefore avoids the potential confound of bias introduced by testing a 'hand-picked' lens from the manufacturer. I hope Bryan chooses to test one or more copies of the lens purchased retail to see if the results align with the copy provided by Sigma.
I totally agree with your views. I was a bit surprised that Bryan published this as a full review and not just a preview. His objectivity takes a hit when he writes this based on a copy provided by Sigma. On the other hand, he still provides what appears to be a frank, open and honest review. I hope he goes back and provides a revision when he get copies through his regular retail channels. I also would have liked to see more image examples.
I have the 50 Art on preorder and I am looking forward to see what it is worth. But my experience with the 35 Art, where the AF perfomance is a bit unpredictable, is that I end up leaving the lens in the bag (if a 35/1.4L II came around, I would definitely try that). If the same thing happens with the 50 Art, and especially because my main reason for getting it is to use it from f1.4-2.8, I'll probablly reach for the Otus instead.