Just completed a usb-nSTEP STEPPER setup using belt drive to turn the focusing ring for camera lenses, and scopes like the WO Redcat that uses a focusing ring. Looking forward to feedback from the Redcat customer, but trying it out on my DSLR, it looks to do the trick! I think its a good alternative to split gears, as one belt can fit various size focusing rings. Tension is adjusted by sliding the STEPPER in/out on its cross bar. I have my DSLR attached to a dovetail bar, and the stepper rides on a crossbar attached to the dovetail bar.