Originally Posted by Greg Chappell
Same comments here as ramcewan. f2.8 just isn't going to produce much in terms of out of focus blur at a 38mm equivalent field of view. You'd need f2 or faster.
As non-pancake primes with modest (bordering on slow for short primes like these) f2.8 apertures, the 19 and 30mm Sigma's are solid lenses optically. Better than kit zooms but they don't have that little extra a faster prime would provide. Of course, they also don't cost what faster primes would cost either, which is their biggest selling point.
Greg I think you hit a valid point, for a short focal length f2.8 simply isn't fast enough to produce a great deal of blur aka bokeh outside the focal plain.
Makes me wonder about the new Panasonic 12-35mm f2.8 zoom. I am reading about more and more professional event photographers who are opting for an OM-D or two along with the Panasonic 12-35mm f2.8 and the Panasonic 35-100mm f2.8. I think it is great that these lenses now exist as they do allow professionals an option for a relatively fast zoom in the most useful focal length (24-70mm and 70-200mm equivalents). I am guessing bokeh isn't much of a concern for them in the lower range and when you get to the 35-100mm range f2.8 is fast enough when combined with telephoto effects to produce useful blur for portrait type shots.
I keep thinking long term I'd like to upgrade to an OM-D and the 12-35mm in place of a bunch of primes, but discussions like this make me think I might not find f2.8 fast enough.