Optically it is nothing short of superb even at fully open aperture. It's extremely sharp with low lateral CAs, low distortions and low vignetting. The bokeh is very smooth. Out-of-focus highlights are rendered nicely at f/2.8 although there is some room for improvement at smaller apertures here.
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we also have to stress again that it is a marvel of a lens in optical terms. The high performance has also to be seen in to the context of a comparatively low price tag. Therefore ... highly recommended