End of February 2012 I bought this lens. Unfortunately, I realized after a few shots already, that the lens is badly decentered. The whole left side image was extremely blurred. Even when stopping down to f10 or f12 was the uncertainty still clearly visible. This is why I sent the lens a few days after purchase to Sigma Germany for adjustment. After about four weeks I got the lens back and again ... something's wrong. This time, the left side is ok, but it is now above all muddy and somehow doppelkonturriert. And I also shows the measurement scale of AF's absolutely incorrect values: 0.5m is at infinity. So I complained about this service and sent back to my lens Sigma. It took a little over five weeks and I got an email from Sigma. There was: "The execution of necessary repair is possible only in our plant in Japan, the processing time is thereby unfortunately delayed by an estimated 4 weeks..." I beg your pardon? After more than five weeks, I should wait another four? Thereupon I where I exhort my defective unit easy to exchange a "bad" email to Sigma Sigma sent to a well-functioning. And indeed, a few days after that, I got a whole new Sigma 8-16 and this copy is perfect.
A well-aligned Sigma 8-16 is really top! It is very sharp even at the maximum aperture at the edges. At 8mm I see no difference between f4.5 and f8, the sharpness is in all parts of the image equally well. The lens hardly CA's and minimal flare in backlit. Autofocus is thanks HSM ensures quiet and pretty fast, at 8mm but hardly relevant.
Sigma 8-16 has a smooth surface in the current version and acts of the processing and feel very high. But it is pretty clunky and not particularly easy.
The front element of the lens is strongly convex constructional reasons. It is therefore not possible to use this lens any filters. Even the front cover of the lens is extra deep.
Conclusion:
I am very happy now to have a good copy of Sigma 8-16. This lens is a must for every ambitious amateur photographer with a 1.5x crop camera. Nevertheless, I find it very unfortunate that Sigma's customers who actually spend a lot of money mainly equipment sold for stupid. Only after really nasty emails and months of repairs is to be understood and the customer gets what he actually paid. But getting out better later than never.
For me now the question arises, how am I to evaluate the Sigma 8-16? My present specimen is clearly worth five stars but if I am to mark the service of Sigma with, then five stars are there excluded. So I forgive four stars, one point deduction will not get the lens but Sigma.
