Autofocus of the tested lens, when joined with the Sony A7R camera, is practically noiseless. Unfortunately, it is also slow. Running through the whole distance scale and confirming the right position takes about 1.5 seconds. Of course the distance range is very wide – after all you deal here with a fully fledged macro instrument. You can try and save some time by employing the focus limiter e.g. choosing a range from 0.5 of a meter to infinity. Still, even then the lens isn't able to reach a good autofocus speed because the whole action still takes about one second.
What's more, while taking macro shots in a shadeless tent we often experienced some focus play – the lens missed the right position on the scale, went back and only then was able to confirm the focus. It lengthened the whole process. Fortunately when we took the lens outside such situations were few and far between.
In a case of a preproduction version of a lens you can be sure in the final product the optical construction will remain the same. Of course in the shop version there might be some changes concerning antireflection coatings or a better blackeninng of the tube but they usually are limited to software. More often than not it means improvement of the autofocus mechanism. We trust that the production version of the Sigma A 2.8/105 Macro will fare better than the specimen we got for our initial testing.
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Looking at the flat front element, situated at the very end of the casing and not sheltered by anything against side light, I had many doubts concerning the performance against bright light. Two other things made me even more wary:a very complex optical system (as many as 24 air-to-glass surfaces) and internal focusing that limits constructors when it comes to including internal baffles that can damp down flares. As you see standards in this category were raised really high.
Photos below prove that the performance of the lens is indeed far from perfect. Still, taking into account the difficulty of the task Sigma constructors faced I think this instrument came away rather unscathed. There are not so many reflections; only in one position, with the sun situated in the very corner of the frame, they can be intensive. Overall, they don't take a lot of space in the frame and aren't very bothersome so the situation looks better than I expected.
