When DSLRs started offering HD Video recording, independent and guerilla filmmakers finally were able to afford to get out of the camcorder ghetto while taking advantage of techniques that utilize depth of field. But what they've really missed was the capability to accomplish a smooth "follow focus," which is the ability to focus from one part in the depth of field to another without causing camera movement. That's where the Okii USB Follow Focus Knob comes in handy.
Compatible with most Canon DSLR cameras, the OkiUSB Follow Focus Knob, is a small, round device with a handful of control buttons and uses the camera's mini USB port to remotely manipulate the camera lens and focus it in and out. The buttons can be pre-set for specific focal points so that the camera will rack focus from each point seemlessly every time. Other buttons are used to start and stop recording, adjust ISO, aperture and shutter speed, as well as changing focus zones. The only downside is that it seems the buttons aren't labled, so the user has to memorize each function position.
To see the USB Follow Focus in action, check out this video from DSLR FilmNoob.
The USB Follow Focus Knob runs about $400, and is currently available pre-order.