"These are all great tips, but no amount of muscle memory or barrel markings are going to help you in the situation described above. The depth of field on a wide open 80mm lens on a 35 adapter with its 1/2000th inch CofC is just not a reasonable amount to work with when shooting a moving human being. Even after taping out, there is no way to judge when an actor has leaned forward as little as 1". In this case it is best to inform the DP of this logistical nightmare rather than sit quietly and hope to get lucky. A professional DP will often plan ahead for these types of situations by lighting to a better stop. Unfortunately with the 35 lens adapters DP's feel they have free reign to stay wide open all the time. The best advice in this situation, is to make sure you have a really good view of the monitor and a 2nd AC who will listen to your complaints afterwords."
Not sure I agree with all of this. I DO agree that the DP is also responsible for focus by lighting to a stop that the focus puller stands a chance with. This stop is on a shot by shot basis and in part depends on the abilities of the 1st AC. I'll assume the stop in question here is a 1.3 because the original poster mentioned an 85 on the PRO 35 adapter and this is what the Zeiss Super speeds open to (I'm ruling out Cook S-4s, Primos, etc. since they are expensive and usually seem to end up on film jobs - big difference, in my book though, between a 1.3 and a 2 though). Was the camera moving or just the actor? It sounded to me like it was just the actor. If so, the 85 is a common lens for CUs and one needs to be prepared to get MOST of it in focus - I say most because it is indeed hard. More experienced film actors tone it down a tad for CUs, but not all, making it hard on the operator and AC alike. When faced with shots like this, you need to figure out a percentage of acceptability, which in a nutshell means how much do I need to nail?
As for it being impossible, I recently shot a bunch of Steadicam footage at a T2 on a 135mm in a boxing ring roaming about between the two boxers. Killer stuff, but I was keenly aware that only moments would be useable.