I had the Sigma 50mm / 1.4 lens at the same time with a Pentax 55mm / 1.4 for testing on my Pentax K-5 is available. The image and build quality is excellent in both lenses, with the Pentax lens at the latter still leaves an impression wertigeren (is also splash-proof and 200 EUR more expensive). For the autofocus when Sigma lens is significantly faster. The Bokeh liked basically good, but comes subjectively not quite the Pentax zoom. Chromatic aberration is in two clearly visible at maximum aperture depending on the subject, but in the acceptable range - this to me is the Sigma compared liked better.
Unfortunately, both lenses had an incorrect focus on my camera. The Pentax of settled neutralize practically by the camera-side lens adjustment, which unfortunately succeeded me at the Sigma only for certain distances. I would therefore have to send for adjusting it, what next to the splash protection was the main reason for me to opt for the Pentax. From the picture quality alone both lenses are highly recommended.
