Motion picture cameras are traditionally all-manual; meaning they do not auto-focus nor are cinema lenses designed with internal focus motors. Because these cameras are quite large and heavy - their use typically requires two or more camera operators.
The Camera Operator (CamOp) handles the framing of the scene, the following of the action, and the switching on and off of the shutter.
The 1st Assistant Camera Operator - is also known as the "Focus Puller". This very important job has to be done in coordination of the CamOp's movements - they operate the FOLLOW FOCUS mechanism and ensure that focus is sharp throughout the shot.
In short - YES - there is such a thing as "auto-focus" on a motion picture camera - it's called a Focus Puller (using a follow-focus).
NEXT - What is a Follow-Focus & how does it work?
A FOLLOW-FOCUS is a device that is designed to allow the Focus Puller precise and smooth control over the adjustment of focus on a cinema lens. Generally, all follow-focus systems work the same way and share a similar design. The primary functions are to allow for smooth movement of the lens focus ring (so there are no abrupt or jerky focus adjustments - which are visible in the footage) and to allow the focus puller to make precise notations of where two (or more) focus points may be during the shooting of any given scene. FIRST - Allowing for smooth focus motion. Any professional-grade follow-focus will have a transmission - a gear box that translates small movements into smooth larger movements. This is to avoid any sudden or jerky motions that might jar the viewer out of their movie-going experience.
SECOND - As I explained in my card regarding "Long Lenses" that sometimes depth of field is very shallow with telephoto (long focal length lenses) and/or lenses that have large apertures (fast lenses). If the DOF for a given shot is 1.5 feet or 18 inches and the primary subject of the shot is moving around, walking back and forth - changing their distance from the camera as they walk, if they move out of that 18" window of focus, the image becomes blurred and ruins the shot. A follow-focus has a white dial on it that can be marked on with a grease pen. This marking dial allows the focus puller to make marks at certain cues during any given shot so they can quickly hone in on their focus points as focus changes.
The follow-focus is a vitally important tool in cinematography that without countless scenes in countless movies and TV shows would have been impossible to film. NEXT - Why do film camera crews need such a device?
MEASURING THE DISTANCE TO THE SUBJECT FROM THE FILM PLANE OF AN ARRI MOTION PICTURE CAMERA.
All lenses utilize distance measurement in some shape or form for focus. New auto-focus DSLR still cameras calculate distances automatically and use this data to move the focus elements of the lens attached to them. Being all-manual - Motion Picture Cameras require the camera crew to make measurements using tape measures. There is a mark on every camera that denotes the physical location of the exposure plane/film plane - where the sensor or negative sits when it is exposed. Measuring from that point to any focus point in a scene gives the focus puller the distance required for proper focus in the shot. There are often marks or places where an actor is expected to move to or away from (deciding these points is a process called blocking), each place has to be noted and the actual distance to the film plane measured. This allows the focus-puller to move the primary control knob of the follow focus to keep the subject in focus at all times. NEXT - What is a rack-focus?
Racking focus is the process of setting two or more focal points in a single shot and then using a follow-focus to move focus between them.
This can add suspense/drama/intensity to a shot. The rack focus above was shot with a very long 300mm lens - the distance pulled was only about 8 inches. By using a follow-focus you can make the marks for these two points corresponding focal positions and then move between them with ease.
NEXT - Do I need a follow-focus?
DO YOU NEED A FOLLOW FOCUS? Honestly it depends. Until recently - professional DSLR HD cameras would only operate in full manual (i.e. no autofocus regardless if it was an AF lens) in movie mode. Only one or two professional-level cameras do allow the option of auto-focus - and ALL professional - cinema HD cameras are full-manual. This honestly isn't going to change. If you allow the camera to decide focus you take away the creative control of the director - who may for creative or narrative reasons want focus to remain on a certain point. You loose the ability to control those points once a camera is allowed to decide them for you. The true determining factors in whether you need a follow-focus or not involve two things. 1) How complex is the shot? If you are shooting with a 300mm f/2.8 lens at 40ft and therefore your subject only has 6 inches or less of focus range and they are going to keep moving between two or three points. Yes - a follow-focus can truly save you immeasurable frustration and wasted time. 2) If the lens you are using has a really long throw - meaning the barrel of the lens requires a full revolution (or more) to go from the closest focus point (the closest point in front of the lens an item will focus) to infinity, then you might appreciate having a gear-box to assist you in making long focus pulls. These two reasons are more than enough justification to invest in a follow-focus. The price of affordable Pro-Am (professional/amateur) quality follow-focus systems has dropped significantly over the past 5 years. Good quality units can be had in the $500-$1000 range. High-end Pro-Am systems may cost upwards of $1500. Cinema-grade/commercial systems such as the ARRI FF-4 (follow-focus 4th generation) can cost several thousand dollars. They are heavy, robust, large, and offer the most flexibility in their use and configuration. They are also complete overkill for a DSLR.
The FOGTA DP500II Follow Focus is a surprisingly well-constructed, full-featured DSLR follow-focus with a smooth transmission and interchangeable drive gears. At around $250 it is a good choice for the film-maker on a budget.
A photo of me setting up an ARRI SR-II super-16 motion picture camera with ARRI FF3 follow-focus on a 2-speed full-transmission geared cinema head - the gentleman with the banana-clip in his hair is a CamOp I've often collaborated with - a very talented professional. As the Director of Photography I am responsible for both the camera and lighting crews. I always do inspections of the equipment to ensure everything is in optimal working condition.
MY FINAL RECOMMENDATION IS -
Gear is expensive - unless you purchase cheaply made-cheaply designed equipment - and my experience with it is that you eventually end up spending more money in valuable shooting time trying to get it to work than if you had just spent the money to get good equipment to begin with. Cameras are heavy - and the more gear you add to them, the heavier they become. This means the more difficulty the CamOp is going to have operating them. I'm all for having gear - but unless you can translate the use of the gear into a direct savings in your production on some other level - rent the gear you need or go without. I've shot many good scenes as a CamOp with no focus puller. I've shoot many good scenes where I had a focus puller and they didn't have a follow-focus. It can be done. Try to be smart about what you are trying to accomplish and if you don't have to waste resources on equipment that you might not need or you can for sure do without, you can use those resources in other areas of your project to make it better.
Photography & Cinematography 101 by Jon Patrick Hyde - © 2015