No more fuel to the fire, but just out of interest:
From the Digital Picture:
"Tamron 24-70mm VC Lens Image Quality - Take 4
Tamron 24-70mm f/2.8 Di VC USD Lens
If you have been following this blog/new page, you know that I have been making a big effort to get good image quality results from the Tamron 24-70mm f/2.8 Di VC USD Lens. This is currently the only full frame-compatible lens available in the 24-70mm focal length range with both an f/2.8 max aperture and Vibration Control - a combination that many of us find very attractive.
Evaluating this lens, as I hinted, has been very problematic. The first lens I bought had a serious image quality issue - Tamron wanted it back for analysis.
The second lens I bought performed well, but was noticeably softer on the right side - the side that shows in the site's ISO 12233 image quality tool. I suspected decentering and sent the lens to Tamron for repair/adjustment.
The lens came back from repair performing worse than before I sent it in. Tamron sent me a shipping label to take a second try at the repair.
The results from the second repair, the fourth test, are now found on the Tamron 24-70mm VC Lens Image Quality page. And, <drumroll>, they look very good!
We spent over a full week testing this lens model for the ISO 12233 chart test alone, but persistence has paid off ... I think we have an as-good-as-it-gets copy in our hands now. This process has not said good things about the quality control for this lens model, but again, the image quality looks very nice to me.
What is not looking good is this lens' AI Servo AF performance. This lens has not been able to accurately focus on subjects moving toward or away from the camera. One Shot AF has been working fine, so this lens has plenty of great uses available for it. More to come."
P.S. I took a look through some of the ISO 12233 charts and compared them with the chief competition (Canon 24-70l II). Wide open, I would give the edge at most focal lengths to the Canon (24mm is debatable and might go Tamron - 35mm strongly favors the Canon) although they are quite close. Interestingly, stopped down to f/4, it would appear that this sample of the Tamron is sharper at all tested focal lengths.