Commlite DSLR Follow Focus
No matter what your camera, this Follow Focus lends to precise focus control of a fixed-lens camcorders, interchangeable cinema lenses as well as video-capable DSLR cameras.
Please see link below for video of the Follow Focus:
The precision-machined Follow Focus system provides repeatable, accurate focusing. It is compatible with any camcorder or DSLR models such as Nikon D90, D300s, Canon 550D 7D, 5D MKII and more