In the best condition, the optics (for UWW) convinces through color reproduction and sharpness. Of course, by design corpse smears compared with standard focal lengths must be made.
But now the rub:
At least half (or a lot more?) Of the Sigma 10-20mm delivered have serious production flaws. These manifest themselves in a most intolerable blur on the left side, probably through a decentering of the lens.
Compensate Halfway can-at least in my lens - this blurring by a withdrawal of the focal length to approximately 12 mm, manual focus and a slight closing of the diaphragm. The autofocus makes the hyperfocal distance rather imprecise indication on the integrated indicator is unreliable.
Since then remains only the exchange - which indeed works great on Amazon - or the lengthy warranty repair at Sigma.
Too bad when Sigma would get this permanent background decentrations under control, would clearly my favorite lens.
