I had two of these lenses and both were crap. Not worth 1200$ at all! Have a look for yourselves.
1.Total lack of quality control, decentred elements.
2. Mega barrel distortion.
3. Vignetting present even at f/11 won't go away.(on full frame)
4. Prone to flare even when the sun is at a 80 degree angle.
5. Acceptable(depending on type of photography), but slow autofocus
If it was in the price range of 300-400$ I would be able to look over the issues it had, but at 1200$(even though i got it for 1045$) stay away from it. I mean it! Tamron junk lenses are made out of pickle or mayonnaise jars.
I made the newspaper, brick wall and quadrant test. They are not the most sophisticated but it sure does show the cheap engineering Tamron is implementing in their lenses.
Have a good look at the top left and bottom right corner. It is so bad as if someone intentionally used the smudge tool in photoshop. Disgusting samples.http://www.flickr.com/photos/22285064@N03/sets/72157630580733610/
I used the 5dm2 camera, shot in raw and processed with Canon software all set to default. The crops are full size.
Here is are some images of the distortions:http://www.flickr.com/photos/22285064@N03/sets/72157630553470686/
As you can see there is heavy moustache distortion at 24mm
at 50mm there still is moustache distorition with slight pincushioning
and pincushioning at 70mm
There is no focal length where the lens is free from distortion
Here is the raw image of the newspaper test 30MB size:http://www.mediafire.com/download.php?sli3l6a82g20mkk
and the jpeg with default processing 20MB:http://www.mediafire.com/view/?3sk3x3gbxf58gif
I have read positive reviews about this lens at the beginning, but all of a sudden the internet is flooded with negative reviews... This is called QUALITY CONTROL at Tamron.
Save your money and buy a second hand lens, or better pay 300-600$ more and buy the original manufacturer lens.
Mainstream manufacturer lens last for a lifetime +20 years if they are looked after. Buy Tamron and expect you will be replacing it in 2-3 years after.
Good luck with your purchase of this lens....