Canon lens MF and follow focus

Has anyone looked into a follow focus rig for the electronic focus lenses?
Once you twist the lens focus ring past infinity or minimum distance, the direct relationship between focus ring position and actual focus is lost. So to work the FF control has to have end stops on the action.
Not only that, but if the relationship between focus ring and MF position is not linear then you can't accurately focus from the follow focus knob at all.
Anyone actually tried it?

These are frames from Canon DSLR video, where AF hasn't got a hope.
So I need accurate MF.
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slipping is probably your biggest worry and as far as I can tell there really isn't a way around it. I would try a focus puller rig like this one: Follow FocusShifter - Lens Mounted Follow Focus for DSLR Video and Photography -
These will let you set stopping points and marks so that you can pre set the focus for certain distances which means you can have some control around the intermediate focus points. you always run the risk of slipping if you are moving too fast, I think the idea is to pre focus on the spots you need. this will give you a higher level of accuracy between points.

Recently I purchased Follow Focus....I love it...Very fast setup....

https://www.youtube.com/watch?v=v9Qgt8UrZJ4#t=41