The 'R' is for 'by-wire'
1 2 3 4 5 6 7 8

The 'R' is for 'by-wire'

Digging further into the lens revealed one of the few conventional parts of the 55-200mm's design: the spring ball-bearings used to provide clicks as you turn the aperture ring. That ring being secured in place with screws, of course. It's a similar approach to the one we saw in LensRentals' tear-down of the Sony FE 35mm F1.4 a little while ago: the ring itself doesn't directly drive anything, its movement is registered with a sensor, then sprung ball bearings are added to provide a stepped feel to the dial. Unlike the Sony, they can't be disengaged.