The focus rail on my rb67 pro s is super smooth but does not stay where I put it if I am aiming up at a steep angle or down at a steep angle. Am I missing something that locks focus?
I've only got the ProSD and it has a lever clutch like locking brake if you will on the left hand knob area. You can tighten to a bit of drag or full on lock. I usually lock it once I've focused no matter what the angle I'm photographing at.