Flickr User Develops Cheap Follow Focus Tool
There's a technique used in film and television called a rack focus. You've seen it before, especially if you watch any police or courtroom dramas. It's a simple trick where the cameraman (or assistant cameraman) moves the focus of the scene from one character to another by quickly shifting the focus of the camera. It's used in places where a cut just wouldn't suffice.
If you can shoot video with your DSLR, you may be interested in trying this trick, but it's difficult to do by hand. A rack focus requires accurate starts and stops. On film and video cameras, a follow focus is utilized to make it all easier. In professional film, it's done with a crank and gears, but several readers have called attention to a nice DIY solution that emulates the real thing for about six dollars.
It's not quite as complex as a true follow focus, but it just might do the trick for the budget conscious photographer. Simply swing up to Home Depot and grab a steel hose clamp and a cabinet knob. Attach the knob to the clamp and the clamp to the camera (not too tight) and you're good to go.
It's not a true follow focus, but it's a cheap and easy solution that'll do the trick well enough. Check out the Flickr Page for more details: Link