The First AC is also known as the focus puller. The First is the crew member who directly works with the camera. Duties include:
Loading digital recording media or film magazines on the camera on film shoots.
Ensuring that the camera operates properly.
Checking for hairs in the gate before any scene is wrapped (film only).
Guarding against flares, light leaks, and any other problems.
Setting the T-stop at the DP’s direction. Also, frame rate and shutter angle.
Measuring the focus distances in conjunction with the Second AC; sometimes focus is set by eye.
Pulling focus during the take.
In some cases operating the zoom control. This is sometimes done by the operator using a zoom control on the handle.
Moving the camera to the next setup, with the help of the other ACs and sometimes the grips.
Guarding the camera against damage or malfunction.
Making sure the proper film stock is loaded, or in digital that ISO and other settings are as they should be.
Calling out the footage so that the Second AC can note it on the camera report (film only).
Focus may be determined by measuring or by eye.
Measuring is generally done in two ways. Cameras have a mark on the side that identifies the position of the film plane. Positioned above that is a stud that the AC can hook a cloth measuring tape onto. Most ACs also carry a carpenter’s metal measuring tape; this is useful for quick checks before close in shots. Laser rangefinders are also widely used. The third method is eye focus. This can be done with either the operator and the ACs or by the First AC himself. Someone—either the actor, a stand-in or the Second AC—goes to each of the key positions. The operator looks through the viewfinder and focuses. Always do this with the aperture wide open (to minimize depth-of-field); with a zoom lens, zoom in all the way, also to minimize depth-of-field and also to be able to see fine detail better.
For critical focus, it may be necessary for the Second to take the top off a small flashlight. The exposed bulb provides an accurate and fast focus point that can be used even in low-light situations. For complex dolly shots, the Second may make tape marks alongside the dolly track, thus knowing that at a specific point he is x number of feet and inches away from the subject. Good ACs are uncanny in their ability to judge distance and make adjustments on the fly.
Good ACs will always go through a mental ritual before every shot: is the T-stop properly set? Is the focus prepared? Is the camera set at the right settings? Are there any flares in the lens? It is best to do it in the same order every time for consistency. In previous times this checklist was remembered as FAST: focus, aperture, speed, and tachometer. Cameras no longer have tachometers, but they do have frame rate controls that must be checked regularly. There are also codecs, recording format, and “Looks” to keep track of. They might be different for frame rate changes as some cameras can’t record maximum resolution at higher frame rates.
from Cinematography: Theory and Practice, Blain Brown
3 SIMPLE WAYS TO BECOME A BETTER FOCUS PULLER OVER THE WEEKEND
Guess and measure distances
The easiest way to become a better focus puller is to become exceptionally accurate at guessing distances. You should strive to become a human measuring tape. The best 1st AC’s will walk into a room and have a real, tangible sense of the space they’re in.
Start by going into a room with any measuring device and sit in the corner of it. Pick an object, write down your best guess for its distance and then measure to it from where you were sitting. Once you know the true measurement, compare it against your guess then really try and get a feel for how far away it is. It is important not just to guess, but to evaluate after the fact to get a sense for what 5, 10 or 15 feet looks like to your eyes.
Once you get good at this you can even move on to guessing depth-of-field by choosing an object, a random focal length, and go through the process of guessing and checking with a depth-of-field calculator. Knowing distances are good, but also knowing how much play you have with depth-of-field is a big part of focus pulling as well.
People watch in public places
You may not always know what is going to happen in a scene because of rewrites or improvisation. Being able to anticipate the natural movements of people can help you subconsciously prepare for unexpected moments in a scene.
Go out to a public place like a park, a mall, or even on the street and start paying attention to how people act, react, and move around certain spaces. When two people are talking do they lean into each other? Do they lean forward before getting up? When someone is walking with a friend, how do they pace themselves?
You should attempt to visit a variety of atmospheres where people will act differently. Intimate settings, like restaurants, are probably the most likely to pop up in movie scripts.
Now, I don’t advise being creepy and stalking people, but pay attention to surroundings and the physical movements within them. That way you build up a certain expectation to how people, and subsequently actors, will react in certain situations.
Pantomime the motions
The easiest way to do this is to sit in a room and put your hand in the air like your gripping a follow focus. Now look at a doorway with your hand ready at your “air” follow focus. Pretend a character is walking in and sitting down somewhere in the room and adjust your pretend follow focus as necessary.
This is good practice because it emphasizes the motion of focus pulling and will get your mind used to the direction in which you must pull to go a certain way within the focal plane. The saying I use is “go back to go back and go forward to come forward.” That means you pull the disc towards you to send focus further distance-wise and move the disc away to bring the focus closer — at least on cinema style lenses.
I cannot overstate how important knowing this concept is to pulling focus. Once you can adjust direction without thinking, focus pulling becomes so much easier.
It can be one thing to gauge a distance, expect a movement, but in the end the follow focus has to be turned in a balletic fashion to coincide with on-screen movement. Get used to these kinds of motions and when you do the real thing, it will be a lot more relaxing.
Practice Makes Perfect Focus
Pulling focus can be intimidating, but it can also be really fun. If you’re having difficulties with it, don’t fret. Even the pros have their bad days.
But if you’re feeling like you aren’t yet the best focus puller you can be, try one or all of these suggestions in the next few days and I guarantee that you will come out on the other side with a better sense of the job.