I decided to write a review of this lens because the user reviews I could find online are quite unfair about the lens, and contain some inaccuracy.
The lens comes very well boxed, and with a good solid lens hood, and a lens pouch. The Italian distributor of Tamron grants 5 years of guarantee, and if your lens faults in the first two years, it is replaced by another new copy. They also give a free professional UV filter. All in all, a very good bargain for 570 Euros.
The build of the lens is solid, made for most part of good sturdy plastics, but with metal parts where they count: the lens mount, and the tripod mount. The lens hood is also made of good quality plastic that will stand most hits.
The image quality is, quite simply, superior: the lens is tack sharp from wide open. Purple fringing is almost invisible, except in extreme situations. The bokeh is smooth even in critical situations such as background of tree leaves; the rendering is pleasantly three-dimensional. Quite impressive optical performance overall.
I was nervous when I bought thia lens, because of the utterly negative reviews that I read about it's autofocus performance. I am a wedding photographer, and although my subjects are not as fast as sportsmen, they are not still either. I can now say that the negative reports are exaggerated. True, the autofocus is not as fast as the ultrasonic kind, and not as silent either. But it's far from the total disaster it is often talked about.
Firstly, it's not really slow as in s-l-o-w. It's just not lighting fast. How fast is it? Well, probably not fast enough to get a running football player. But surely fast enough to catch movement at a wedding party, or on the street. So, it really depends on the use you will make of it. If you do weddings, like me, buy it safely, it will do the job.
One inaccuracy I often find in the reviews of this lens is, how unuseable it is in low light. It is not my experience. My copy (made in Japan) focuses well even in low light, just a little slower than in day light. I never experienced the "focus hunting" often reported, *except* when starting from a very different focusing distance. In that case, the lens often gets stuck and does not focus. BUT, this does not happen in low light, it also happens at noon. It is a limitation of this lens *unrelated* to the amount of light. The solution is simple: just prefocus manually the lens in the distance range of your subject, then switch to AF. Alternatively, if you are at 200mm position, move to 70mm then try focusing, in most cases it will work; then move back to 200mm.
Speaking of focusing performance in low light, my copy does focus correctly even in situations like ISO3200 F/2.8 1/6th shutter time.
Which equals to a practical = *always*, because, you will never shoot this lens hand-held with those settings: you'd get an unuseable photo.
Which leads to the real shortcoming of this lens: the lack of image stabilization. But hey, the lens costs less than half than the stabilized version, and almost 4 times less than the Canon equivalent!
Also, image stabilization is not the magic wand: you may shoot at 1/30th with it, and get still tables, but the people in your wedding party, unless already drunk, will surely move faster than the 1/30th speed can handle. So, once again, it's not all that tragedy again. The truth is: when light is too low, use your F/1.4 50mm lens, and crop if necessary. End of story.
This lens is a great bargain; at around 600 USD, or less, it offers an image quality that is on par with the 2300 USD worth Canon equivalent. You will not shoot basketball games with it, but if you do portraits, wedding candids, street photography, you'll be perfectly fine, and will save 2000 USD.
Would I buy the Canon lens, if I had the money for it? Yes, no doubt.
But the reason I write this review, is that many people, who would not need extreme AF speed for their shooting habits, give up buying this lens because of the catastrophic reviews about it that they read online. My message to them is: if you need a 70-200 lens, and have 600 dollars in your pocket, do not give this lens up because in maybe two years from now you'll have gathered the money for the Canon; buy this lens today instead, and start shooting. You'll take beautiful photos.