You can't pull focus without measuring for it first, so today I want to dive into how to approach that so when you whip out a tape measure on set, you know what you're doing.

There’s a reason why the 1st assistant camera (AC) is also called the “Focus Puller.” It’s because that single responsibility of keeping a subject in focus is so incredibly valued, that there is an entire job, an entire career, devoted to it.

Yes, focus pullers and 1st AC’s have more to do than spin a disc attached to a lens for 12 hours a day, but this single act is the most noticeable contribution that we make to a film.

But you can’t pull focus without measuring for it first, so today I want to dive into how to approach that so when you whip out a tape measure on set, you know what you’re doing.

Why Measure for Focus?

Because focus is set and determined through distance. Without getting into lens optics, you are essentially telling the lens which light rays at a certain distance you want focused on the film or sensor plane.

Because your eyes will never be as accurate as your tools. You can become exceptional at guessing distances, but nobody will ever be as precise or accurate as a trusty tape measure. Guessing the distance and knowing the distance are two different games when it comes to pulling focus.

Because even to this day it is still the most dependable way to keep a subject in focus. As long as the back focus on a camera is set correctly, you won’t have a subject standing at 8 feet out of focus when you set the lens to 8 feet. Simple.

Before the crisp monitors of digital cinema cameras and the improved monitoring of modern film cameras, distance marks were pretty much how you pulled focus. There was no monitor to crutch on, there was no peaking — it was your tape measure, your eyes, and the lens.

How to Measure for Focus Marks

It seems silly for me to give a tutorial to you on how to measure a distance, but measuring for focus isn’t a simple A to B process. There are many considerations such as what to measure and when it’s appropriate.

If you don’t know what you’re doing, you risk wasted time and soft footage.

1. Start at the Film/Sensor Plane

The measurement for any shot begins at the film/sensor plane of a camera which rests behind the lens and its true location is designated by a “Phi” mark on the body of the camera.

The only time that you won’t measure from the film/sensor plane is when you are using ENG (Electronic News Gathering aka TV/Broadcast) lenses. These can be easily identified by a green stripe around the barrel. With ENG lenses, you measure from the front of the lens.

2. Measure to Each Subject in the Scene

The next point of measurement is going to be the subject you are focusing to. If there are multiple subjects in a scene, you will have to take multiple measurements. Most of the time the subject is a character, but often times it is not. It can be a door handle, a telephone or even a skeleton on a road.

Whatever the subject is, you measure to the part of it that you want in focus. This is a crucial concept. You can’t measure simply to the subject itself. In some scenarios, your depth of field could be very shallow meaning only parts of a subject will be in focus.

That’s why you measure to the most important part of a subject to be in focus. For humans, this is the eyes.

It would look funny if the tip of somebody’s nose was in focus and their eyes weren’t. Or if their ears were in focus, but not their face.

See what I mean now?

3. Measure to a Few Reference Objects

Let’s say you’re about to film a fist fight in the living room of a house. The fight is choreographed, but the blocking is fairly loose. The director tells the actors to play freely in the space, so in rehearsals they sometimes fight 6 feet away and other times 9 feet away and they’re never consistent.

How do you measure for this?

You get yourself some reference marks by finding points in the room that you can measure to. Then, during the scene, match the position of the actors to those references and adjust your focus.

Is there a couch they are fighting near? Or a table? A bookshelf perhaps? Look for any object that is in your view from beside the camera and that gives you a clear indication of the actor’s relation to it.

It’s best if you have get reference marks in front of, beside, and behind the points of action. This way you are prepared for any and all scenarios — including the unexpected.

And there’s always an unexpected moment in every scene. Trust me.

4. Transfer Your Marks

The final step is to transfer your marks onto the lens, follow focus, or to your “mental map.”

The most important marks, such as character landing marks will go on your lens or follow focus, while less important marks, such as reference points, you make a mental note of.

If you make enough of these mental notes, you build a “mental map” of the room in your mind.

Pulling Focus Starts with a Tape Measure

Measuring distances and getting those marks is the first step towards successfully pulling focus. You can judge focus off of monitors and viewfinders, but it is not as dependable as setting the lens to the precise distance the subject is at.

Being able to pull focus by distance is a skill that eludes many camera assistants for a long time as they constantly try and improve themselves. Whether you consider yourself a camera assistant or a focus puller, this is a valuable skill that, in many ways, will define your career.

And it all starts with a few simple measurements.

How many marks do you take measurements for on set? Do you have a minimum amount of marks you like to get? A maximum? Please let me know in the comments below.