Panic

Olympus's M Zuiko Digital ED 12-40mm f/2.8 Pro lens is a fantastic constant-aperture zoom that covers wide-angle to portrait focal lengths with a fairly fast maximum aperture and is good for all but the dimmest indoor settings. I've had good luck with it in the classroom at last weekend's FPF Training class in Terre Haute as well as shooting "grips & grins" type shots at the Tac-Con presenter's dinner the weekend before.

It uses a pretty slick selector to switch back and forth between auto and manual focusing: Slide the manual focus ring to the rear (there's a slight detent) and it exposes the focus range numbers on the lens barrel. Now you're in manual mode.

The downside is that if you do slide this ring back inadvertently, it can take you a good fifteen minutes of panicked digging through the camera's menus and turning it off and on again, all while thinking you've somehow bricked your very expensive lens, before you realize what's up.