I had a chance to try this lens out today (on a D3) for a portrait assignment at the Dallas Four Seasons Hotel of the head chef. Just a one-light with umbrella, and fill card, slow shutter, pretty wide-open shot. I have to say I had somewhat of a hard time with this lens for my first round with the AF. Maybe because I was using a strobist setup, hence no modeling light and therefore low-light and wide open, but about half the time the lens/camera just refused to lock on. I ended up trying manual part of the time, and winged the rest. I guess to be fair, I need to work with this lens a little bit to get a better feeling for the focusing in lower light situations. Anyone else come across this type of sluggish AF?