So I just opened up the lens I got in the mail. Nothing else looks questionable, but the autofocus does not work. I'm starting to think I made a very elementary mistake or did something otherwise stupid. I'm pressing the shutter button halfway down with the AF switched on, but there's no noise or any kind of movement. There are two focusing "barrels" I guess, both of which need to be turned manually to get the image into focus. When switched into manual mode, I have to do the same thing to get a sharp image, so I see no change. The electrical contacts look clean, and I'm pretty sure I'm snapping the lens into place correctly. I really don't know what's going on, so some help would be appreciated. Thanks a lot!