It's easily my best "bang for your buck" lens. My 70-200mm f4L is probably my sharpest lens, but the 40mm f/2.8 is right there with it. Its auto focus is just fast enough to work with moving subjects. This is my most recent example-- sort of an experiment, and I don't think I'm quite satisfied yet. I was going for some kind of middle ground between photograph and colored pencil sketch. Anyway, it's a really useful, surprisingly versatile focal length for museums and general walk-around use. Wide enough on FF to get context but "normal" enough to closely frame subjects without worry too much about distortion.