The mark, and the actor’s ability to land on it, affects the focus and the composition. Some actors and actresses, however, are not the most adept at always landing on their marks (as Michael Caine is) and that means adjustments have to be made. Here’s one way to deal with talent who consistently miss their mark.
To clarify, when I say “consistently miss their mark,” I don’t mean they always go a foot over or 4 inches in front of the mark — that adjustment is easy to make. I mean they consistently just plain miss it. I’ve dealt with this before, with the lead actor no less, who would always miss his mark but never at the same distance.
Despite repeated attempts to remark him where he actually landed, it never worked because he would then miss the new mark. I began to think he misunderstood how to utilize the mark in respect to his position. Nonetheless, a camera assistant shouldn’t complain and should do their job and part of the difficulties of that job is having to compensate for situations like this on-the-fly.
What I started to do was right after rehearsals ended, I would politely ask the actor to do whatever action it was leading up to him hitting his mark and to stay wherever he landed. But instead of remarking him, I would simply set a new mark on my lens and tell him I was confirming the previous mark. I figured that having him do the action would get him to land in a more natural place than asking him to stand at the mark itself.
I was right — almost every time I used this tactic, he would miss the mark, but the focus would be spot-on thanks to the new distance I had measured out. So, if there are troubles with an actor hitting their mark, but all the usual approaches and reminders haven’t helped, ask them to rehearse the scene naturally and use this as a mental reference point.
Now this won’t always work, I realize. Sometimes the mark is just missed and sometimes you can adjust for it, other times the subject gets soft. All AC’s are human and when shooting wide open on a 100mm, there are bound to be some buzzy takes without some help. But at least this tactic gives some kind of hope that your mark will be right on the money. If that still doesn’t work out, consider downgrading to 2nd AC, they get all the love anyway.