I've always wanted the Sigma 30mm to provide the equivalent of a 'fast fifty' on APSC - more concerned with shallow DOF and background blur than speed per se. I have a copy of the lens now, and must say that it certainly does blur the background more than my Pentax 35mm f2.4. However I am not to sure about the quality of the bokeh - there's something ragged and 'triangular' about it:
Sigma 30mm f1.4:
Pentax 35mm f2.4:
Sigma 30mm f1.4 bokeh crop:
Pentax 35mm f2.4 bokeh crop:
So the Sigma wins on quantity of the bokeh, but the Pentax beats it hands down on *quality* I'd say!
With the subject at closer range, the background is blurred more, and the Sigma's bokeh problems go away:
So I am more impressed with it for portrait use than for medium range shots. On the other hand the background separation on the car shot above is hard to achieve on APSC, even if the Sigma doesn't do the job as smoothly as I would like.