That is a good point about the shape of the blades, John, though of less importance when the lenses are used close to wide open, as they often will be.


Actually, I don't understand why the f/1.8 looks so much better in Bryan's examples, despite having blades that sound inferior to the sigma. Neither lens has funny bokeh-enhancing correction (that I know of), so I would have thought aperture blades would tell most of the story. But then, there is plenty I don't understand about optics. (I'd love to hear from someone who can explain something of how factors other than shape of aperture blades and spherical under/over correction can bokeh)