Photozone: "superb" Pentax SMC D-FA 50mm f/2.8 macro

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