From Camera Technica, a pair of videos showing the aperture blades of a Canon 18-55mm kit lens - the kind of lens you get in a cheap DSLR bundle - opening and closing in slow motion. The mechanics of even this cheapo lens look amazingly sophisticated seen like this.
Aperture blades must not only be precise in the amount of light they allow through, they must be lightning fast. In the split second that you press the shutter button, the razor thin aperture blades must close to a precisely sized hole, await the shutter exposure, and then snap back into the wide open position before you can blink your eye.
Eye-opening, in a manner of speaking.