This $400 knob proves that the SLR really is the movie camera for today's indie filmmakers. It's called the Okii Systems USB Follow Focus, and it does what it says, allowing you to control the focus ...

Focus rings let you manually adjust the focus of your images—video too, on select DSLRs—but they aren't particularly smooth. A DIY focus knob gives you finer control over the range of focus. Photo by ...