I've just bought the 15mm f1.7, to add to my prime collection of 20mm, 30mm, 45mm and 60mm. Out of that lot, not a single lens (Well, maybe the O45 is damn close) is advertised as an equivalent of one of the classic 35mm focal lengths. This seems to put off a significant number of people - i've read reviews giving the lenses a black mark just because the focal length doesn't fall into a 35mm category, and the furore (not on this site) about how the sigma 30mm is too long for one thing and too short for another is bordering on the evangelical. I'm not saying that having a wide, standard and tele isn't important, I just don't get why 28mm, 35mm, 50mm and 85mm specifically are so special. So what gives? Why are these focal lengths so important for anything except a legacy from a bygone age? Surely, especially in this day of excellent zooms, it's become nothing more than another number, and having decent coverage across a variety of focal lengths is more important than falling into some neat category from a system that belongs in the past? Opinions welcome.