Follow focus on cinema camera? I would like to purchase a Blackmagic camera but it doesn't have any follow focus system. When searching further, I noticed that many professional cinema cameras doesn't have an integrated follow focus system (Arri, Red...), while a basic Sony A7sii does have one.

I would like to know please how do these cameras work. I saw that they are used with a separate follow focus system (be it wired or wireless) but technically when an object is moving, should the operator grope and try to match the focus on the moving object or is there any automatic recognition system ?

Thanks, 
Cheers
On professio al sets with a camera crew, there is an extra person which pulls the focus.
We don't really use automatic focus.
This needs some training, but it's not so hard to pull off.

Normally, you attach 15mm rods to the camera body, on which you then mount the FF system, "wired" systems start at around 20$, useable ones at around 100$.

Wireless you could take a Tilta Nucleus Nano for 230$