Quick description of a home-made follow focus
A) Marking board
1)measure the outer diameter of your lens
2) cut a ring in a piece of cardboard. The inner circle of the ring should be the same size as your lens
3) If the ring is a bit loose, cut a notch in the bottom of the ring, use another piece of cardboard to bridge the gap and tighten the ring at the same time.
4) cover the ring with white paper (cheap, easily replaced)
1) cut a piece of plastic coat hanger approximately 3-4inches long
2) stack three small pieces of cardboard (1x1.5in) and hold them together (I used duct tape)
3)punch a whole through the middle of the cardboard stack slightly smaller than the diameter of your coat hanger piece
4) Jamb the coat hanger piece into the cardboard - add duct-tape to reduce wiggle
5) measure a piece of double sided velcro to fit around your lens's focus ring plus a few inches of overlap
6) cut a fourth piece of cardboard (1x2.25in) and measure it to fit under the cardboard stack with the sides folded up
7)Where the sides fold up, cut a slit just wide enough to fit the velcro
8) thread the velcro through, attach the cardboard and velcro firmly to the whip with duct tape
now you're ready to rack focus!