Follow focus
Encyclopedia
A follow focus is a focus control mechanism used in filmmaking
with film
cameras and in television production with professional video camera
s. It is ergonomic rather than strictly necessary; in other words it does not contribute to the basic functionality of a camera but instead allows the operator to be more efficient and precise. It is usually operated by a focus puller
(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).
The mechanism works through a set of gears on the follow focus that are attached to teeth on the focus ring of the lens
. These gears feed to a wheel which, when turned by a focus puller, will spin 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. 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.
A manual lens is usually a requisite for professional filmmaking
. This is because some autofocus
lens systems use lasers or infrared
beams to measure the distance between the lens and the subject. This technique does not anticipate an actor stepping into the foreground of the frame, nor can it focus on anything which is not in the center of the frame. Passive Autofocus (not needing lasers or infrared beams) systems cannot always adjust quickly enough to sudden changes. The job of the focus puller then is to adjust the focus onto different subjects as well as change, or (follow) focus during movement of the camera onto the required subject, hence the term.
A follow focus is usually a compulsory piece of equipment for professional filmmaking, although those with low/no budgets or cameras not equipped with detachable manual lenses will have to do with autofocus systems or turning a lens ring by hand. To make matters worse, most 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 electronics inside the camera which predict how the focus should go depending on how fast or far the ring was turned. These lenses make precise and repeatable focus pulls difficult, and use of a follow focus impractical. They are sometimes called "servo" focus lenses or "focus by wire" cameras.
Filmmaking
Filmmaking is the process of making a film, from an initial story, idea, or commission, through scriptwriting, casting, shooting, directing, editing, and screening the finished product before an audience that may result in a theatrical release or television program...
with film
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
cameras and in television production with professional video camera
Professional video camera
A professional video camera is a high-end device for creating electronic moving images...
s. It is ergonomic rather than strictly necessary; in other words it does not contribute to the basic functionality of a camera but instead allows the operator to be more efficient and precise. It is usually operated by a focus puller
Focus puller
A focus puller, or 1st assistant cameraman, is a member of a film crew’s camera department whose primary responsibility is to maintain image sharpness on whatever subject or action is being filmed....
(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).
The mechanism works through a set of gears on the follow focus that are attached to teeth on the focus ring of the lens
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
. These gears feed to a wheel which, when turned by a focus puller, will spin 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. 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.
A manual lens is usually a requisite for professional filmmaking
Filmmaking
Filmmaking is the process of making a film, from an initial story, idea, or commission, through scriptwriting, casting, shooting, directing, editing, and screening the finished product before an audience that may result in a theatrical release or television program...
. This is because some autofocus
Autofocus
An autofocus optical system uses a sensor, a control system and a motor to focus fully automatic or on a manually selected point or area. An electronic rangefinder has a display instead of the motor; the adjustment of the optical system has to be done manually until indication...
lens systems use lasers or infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
beams to measure the distance between the lens and the subject. This technique does not anticipate an actor stepping into the foreground of the frame, nor can it focus on anything which is not in the center of the frame. Passive Autofocus (not needing lasers or infrared beams) systems cannot always adjust quickly enough to sudden changes. The job of the focus puller then is to adjust the focus onto different subjects as well as change, or (follow) focus during movement of the camera onto the required subject, hence the term.
A follow focus is usually a compulsory piece of equipment for professional filmmaking, although those with low/no budgets or cameras not equipped with detachable manual lenses will have to do with autofocus systems or turning a lens ring by hand. To make matters worse, most autofocus lenses with a focus ring (such as those on most consumer and prosumer
Prosumer
Prosumer is a portmanteau formed by contracting either the word professional or less often, producer with the word consumer. For example, a prosumer grade digital camera is a "cross" between consumer grade and professional grade...
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 electronics inside the camera which predict how the focus should go depending on how fast or far the ring was turned. These lenses make precise and repeatable focus pulls difficult, and use of a follow focus impractical. They are sometimes called "servo" focus lenses or "focus by wire" cameras.
See also
- Racking focusRacking focusRacking focus in filmmaking and television production is the practice of shifting the attention of a audience of a film or video by changing the focus of the lens from a subject in the foreground to a subject in the background, or vice versa...
- Follow shotFollow shotFollow shot or tracking shot is a specific camera shot in which the subject being filmed is seemingly pursued by the camera. The follow shot can be achieved through tracking devices, panning, the use of a crane, and zoom lenses resulting in different qualitative images but, nevertheless, recording...
- Homemade Follow Focus Rig