If there's a single received idea that fires up the imagination of my young photographer friends these days, it's that for "professional looking" photographs they should buy fast lenses and then use them at their widest apertures. I've begun hearing them criticize slower lenses and smaller sensors for their lack of "depth of field control." That term once meant something more subtle—we'll come to that in a moment—but now it seems to have become merely shorthand for "Right, let's see how shallow this thing can focus." It's all about blur, baby, blur...