this guy directly coupled it
http://www.philip.davis.dsl.pipex.com/focusser.htm
quote
"The full range of the focus tube, from one end to the other, is in the order of 500 steps so focusing can be quickly achieved using the larger steps first followed by the smaller step and finally the smallest step.
Since the distance travelled by the focuser, from end to end, is around 60mm this means that each step of the motor is equivalent to 0.12mm. I could have wired the stepper driver to allow 400 steps per revolution which would have halved this figure to 0.06mm per step!"
i am very interested in how accurate this focusing has to be? ie is .06mm too coarse?