{{unreferenced, date=September 2008 A follow focus is a focus control mechanism used in

filmmaking Filmmaking (film production) is the process by which a motion picture is produced. Filmmaking involves a number of complex and discrete stages, starting with an initial story, idea, or commission. It then continues through screenwriting, cast ...

with film cameras and in

television production A television show – or simply TV show – is any content produced for viewing on a television set which can be broadcast via over-the-air, satellite, or cable, excluding breaking news, advertisements, or trailers that are typically placed be ...

with

professional video camera A professional video camera (often called a television camera even though its use has spread beyond television) is a high-end device for creating electronic moving images (as opposed to a movie camera, that earlier recorded the images on film). ...

s. It is ergonomic rather than strictly necessary; in other words it does not contribute to the basic functionality of a camera but instead helps the operator be more efficient and precise. It is usually operated by a

focus puller A focus puller or first assistant camera (1st AC) is a member of a film crew's camera department whose primary responsibility is to maintain the camera lens's optical focus on whatever subject or action is being filmed. "Pulling focus" refers t ...

(often called the 1st assistant camera, or 1st AC) but some camera operators prefer to pull their own focus (the act of changing focus is called "pulling" or racking focus).

Overview

Manual focusing is usually a requisite for professional

, because

autofocus An autofocus (or AF) optical system uses a sensor, a control system and a motor to focus on an automatically or manually selected point or area. An electronic rangefinder has a display instead of the motor; the adjustment of the optical system ...

systems may focus on undesired objects, or fail to adjust quickly enough to sudden changes. The job of the focus puller then is to adjust the focus onto different subjects as well as maintain focus during movement of the camera relative to the subject. The mechanism works through a set of

gears A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic p ...

on the follow focus that are attached to teeth on the focus ring of the

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...

. These gears feed to a wheel that, when turned by a focus puller, spins the teeth and thus the ring on the lens. Practically, the device is not necessary as the operator can directly turn the ring on the lens. However, this would place the hand in an awkward position perpendicular to the camera rather than parallel, and turning beyond a certain distance (such as 360 degrees) would be impossible. Sometimes, such a "focus pull" would even be difficult with a follow focus, so an L-shaped metal rod called a speed crank can be attached in the provided square hole at the center of the wheel. Thus, the hand merely has to spin the rod, which turns the wheel. If it is necessary for the operator to stand a short distance from the camera, e.g., if the camera is inconveniently high, a short flexible cable called a "focus whip" can be used. The stationary white disk surrounding the wheel is used by the focus puller to jot down marks, and take care of the focus according to the marks he/she took during rehearsals. A focus puller often uses a tape to correctly measure the distance from the lens to the subject, allowing for accurate marking of the disk. Some autofocus lenses with a focus ring (such as those on most consumer and prosumer camcorders) are not "true" manual focus lenses—meaning that turning the ring does not directly adjust the elements inside the lens, but rather actuates the internal camera electronics that adjust the focus point. Such lenses are sometimes called "focus by wire," and the behavior then depends upon the software algorithm used by the lens. If the focusing algorithm only considers the ''distance'' the focusing ring is turned (called ''linear'' focus-by-wire), then the behavior of the lens is very similar to that of a manual-focus lens. However, certain implementations of such a system also consider the ''speed'' with which the ring was turned (called ''nonlinear'' focus-by-wire), which can make precise and repeatable focus pulls difficult, and use of a follow focus impractical.

Overview

See also