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I have the Tamron. It's very, very sharp. I also have Canon 17-55 and the Tamron easily holds its own with respect to sharpness.
As for testing. Don't try a hurried test in the store. It will tell you nothing. Most shops have a return policy (1 day, a few days, a week). Ask about it, then take your lens home and test it properly, on a tripod, with live-view, being 100% certain that you're perpendicular to the wall, etc.
[quote name='backcountryskier' timestamp='1300212177' post='6824']
I have the Tamron. It's very, very sharp. I also have Canon 17-55 and the Tamron easily holds its own with respect to sharpness.
As for testing. Don't try a hurried test in the store. It will tell you nothing. Most shops have a return policy (1 day, a few days, a week). Ask about it, then take your lens home and test it properly, on a tripod, with live-view, being 100% certain that you're perpendicular to the wall, etc.
[/quote]
I understand your point, however I would like to make sure that the lens I am buying has no easy to spot defects. If is has severe BF/FF issues, to an extent that it can not be corrected on the K-5, than I do not want to buy it in the first place.
Regarding the differences between the Sigma 18-50 2.8 EX DC and the Sigma 18-50 2.8 EX DC Macro, the latter is believed to be significantly improved optically with better corner sharpness wide open and less CA. It also has a larger filter ring (72 instead of 67 mm). It it to bad that a lot of people on the net mix these two up, but here on Photozone you can read that the second version is indeed better. According to Photozone and other reviewers the new Sigma 17-50 2.8 EX DC OS HSM (what's in a name...) is really good and slots right in the top of the class, but here it is also twice as expensive, it is 100 grams heavier and I do not really need nor want OS as it also consumes battery power. And off course it is out of my budget...
I will test the Sigma tomorrow in the shop and if I do not like it, or if it has easy to spot issues, I will check out the Tamron option. Thanks for all your help and thoughts!
