The first two were definitely unusable. Unfortunately, the iNet is full of such reports.
From f 4 good performance, from 5.6 very good, open slightly soft edge and weak, even to APS-C sensors. Pretty beautiful bokeh, which is representation blurred areas, so good for portraits, etc. suitable. Yet handy and not too heavy. Spindle driven AF bit critical at maximum aperture due to high scattering, in spite of good cameras (Pentax K-5 II and K-3), interestingly, from f / 4 no conspicuous problem more.
An attractively priced offer to reportage and portrait region where the WW-field (to APS-C) not going out and above the 75 mm are quite valuable. The only known to me and recommended alternative is the new Sigma 17-70 / 2.8-4 C.
