I spent another several hours reshooting some very nice material with vibration control (VC) disabled. I had some high quality material (or so I thought) to compare with the Nikon 14-24.
But the Tamron has delivered focus problems: even though 10X Live View showed crisp focus, the lens somehow delivered focus badly off even as the Nikon 14-24mm remained spot-on (focus shift aside) doing the same darn thing. Multiple instances of errors, not a one-off issue. It’s as if the Tamron lens glitches somehow, and destroys focus. Immensely frustrating. At this point, I’d advise caution on the Tamron, though that’s a weak point: it could just be a bad sample and it looks to have strong optical potential.
At least three scenes show a severe left/right skew in the plane of focus in the 20mm to 24mm range. Maybe it has a loose lens element or some such thing that accounts for both issues.
And so my review of the Tamron SP 15-30mm f/2.8 Di VC USD must be delayed: I’ve requested a replacement sample and that should arrive in mid April (B&H is closed for Passover). No point in testing a bad sample.
As an aside, the Tamron 15-30mm f/2.8 is very much NOT parfocal; the slightest change in zoom throws the focus substantially off.