This parameter only valid when you set setFocusMode to MANUAL, it is setting image distance, not focal distance.
- Set to 0 means Far end, the image quality is bad.
- Around 60 means INF end.
- Every lens has different property, INF range may be between 40 to 80.
- You cannot use any formula to calculate what value you should set in setFocusRingValue. Since this is MANUAL mode in focus, we suggest you design a slide bar to set the FocusRing manually.