You can make a seup like below using a bamboo skewer so you can detect incremental movements of the servo. I found that a standard servo is capable of ~426 discrete movements in its ~190 deg rotation range. Servos have an internal dead band which can limit resolution. I found that ~5us is pretty mich the lower us resolution limit.
I would think the resolution would be limited by the relatively small pot used by the servo to determine its position.
Better resolution is available through a bell crank or similar mechanical arrangement that swaps range for resolution.Duane B
Check any R/C site for details of cranks.Why don't you tell us what you're trying to do?Maybe there's a better solution.
How are you doing the drive coupling?I was imagining something like the split-band drive around the focus ring.Split-bands were used on old HDDs which had stepper motors to move the heads before voice coils became common.