Tamron 24-70 2.8 VC - issue

I have not noticed any troubles with aperture yet, but VC seems to be a real problem.

I shot a still object at 70mm @ 1/30 sec with and without VC. Without VS I get much better result.

I repeated the test several times with similar results. I get sharp images with that exposure when shot handheld, but maybe one of ten sharp shots with VC turned on.

With VC I get smeared letters, and it looks not like hand-held-long-exposure-blurred (one or two directions smear), it is more like not-in-focus-blurred.

Fitst I thought it was D600's AF to blame, but now it is clear it is stabilisation of Tammy.

I will post some examples later.