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Video Production Glossary
Follow Focus
A follow focus is a piece of equipment that
attaches to the focus ring of a manual lens via a set of rods on the body of
a film or video camera. 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 1AC) but some camera operators prefer to pull their own focus (the act of
changing focus is called "pulling" or "racking" focus).
A manual lens is usually a requisite for professional filmmaking and video
production. This is because auto focus 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 centre of the frame.
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.
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 who 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 can be attached in the provided square hole at the
centre 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 follow focus is usually a compulsory piece of equipment for professional
filmmaking and video production, although those with low/no budgets or
cameras not equipped with detachable manual lenses will have to do with auto
focus systems or turning a lens ring by hand. To make matters worse, most
auto focus 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
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