It seems that in terms of lenses originally built for full frame, 100/105/85mm lenses are more likely to have good background bokeh than 50/55mm lenses, presumably because the former are more likely to be used for "portraits" where nice background bokeh is desireable. But when adapted for micro four thirds, 50mm is a good portrait reach. I have a 50/1.4 Pentax lens (actually I have both a late SMC Takumar and a Pentax-M SMC of the same lens) and the background bokeh is somewhat harsh, with sharp, ringed edges while foreground bokeh (objects in front of the focal distance) is smooth - the opposite of what you'd want for portraits. Anybody know how I'd go about searching for a relatively fast 50mm with more positive background bokeh? How does lens design affect this? Is there a technical reason why most fast 50s don't have as good background bokeh as fast 100s?