Boris Liberman escribió:
5. Sigma 18-50/2.8 - well, I just don't quite like Sigma, and certain people call Sigma really nasty names
There are two versions of that lens. I have the newest, Sigma DC EX 18-50 2.8 macro. This one has a 72 mm. filter ring, instead of 67 mm. in the oldest version, and focuses closer. This lens is a very good one, at least the copy I have. Very good sharpness, except at 18 2.8, where it has good centre sharpness and acceptable resolution at the corners of the frame. Barrel distortion at 18 mm. is noticeable when there are straight lines close to the periphery of the picture, but if it bothers you it can be straightened easily in postprocessing.
It is solidly built, better than the Tamron. I think that the Tamron 17-50 may have a slight edge in image quality, but not much, however a lot of users have reported focusing problems.
The old version of the Sigma lens is still in stock in several shops. I wouldn't buy it, it shows more CA, more vignetting and less sharpness than the new version.
In Europe, the Tamron 17-50 2.8 is about 15% cheaper than the Sigma. I went for the Sigma because I could buy a LN in box lens for a low price (200 euros). I also thought of the Pentax 17-70 4.0 SDM, but although it seems a good lens, it is overpriced IMO. If it had been possible, I would have bought a Pentax DA 16-50 2.8, but this one was out of my price range. In fact, I still would choose that lens over the others in spite of that Photozone review. I don't dispute the findings of the review, but I am sure that a good sample of the DA 16-50 is a better lens than my Sigma EX, which is very good as I said previously. In fact, it is my second Sigma EX series lens, and both have been satisfying tools (the first was a 70-200 2.8 HSM in Nikon mount).
As you see, nowadays quality controls seem to be a thing of the past. Nikon users also have reported problems with the Nikkor 17-55 2.8.
I think you have made a good choice with the Tamron you have ordered. If its AF doesn't work as expected, you can always have it replaced. In fact, I am also thinking about buying a Tamron 17-50 2.8, although I would keep the Sigma, then my wife and me would have a fast walk around zoom for each.
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