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Television Production & Broadcast Journalism
Copyright Goodheart-Willcox Co., Inc.
Pre-Focusing Zoom Lenses
A zoom lens cannot be focused while it is in the “zoomed out” posi-
tion. Focusing a zoom lens is a three-step process called
pre-focus. To pre-
focus a zoom lens:
1. Zoom in on the farthest object on the set that must be in focus in
the shot. The farthest object that must be in focus might not be the
background. For example, picture a cowboy on a horse on a prairie
with the Rocky Mountains in the background. The farthest object
in this shot that must be in focus is most likely the cowboy, not the
mountains.
2. Focus the camera on that object.
3. Zoom the lens back out.
Everything remains in focus until the camera is moved toward or
away from the object of the pre-focus, or until the lighting on the set is
changed.
Many cameras offer a macro setting for the lens. The macro feature
allows the operator to focus on an object that is very close to the camera,
almost touching the lens. The relationship between a fully zoomed-in lens
and a macro lens is similar to the relationship between a telescope and a
microscope.
Depth of Field
The closest an object can be to the camera and still be in focus is the
minimum object distance (MOD). Minimum object distance contributes
to depth of fi eld.
Depth of fi eld (DOF) is the distance between the closest
point to the camera that is in focus and the farthest point from the camera
that is also in focus, Figure 4-5.
pre-focus: A three-step
process to focus a zoom lens.
1) Zoom in on the farthest
object on the set that must be
in focus in the shot. 2) Focus
the camera on that object.
3) Zoom the lens back out.
macro: A lens setting that
allows the operator to focus
on an object that is very
close to the camera, almost
touching the lens.
minimum object distance
(MOD): The closest an object
can be to the camera and still
be in focus.
depth of field (DOF): The
distance between the closest
point to the camera that is in
focus and the farthest point
from the camera that is also
in focus.
The average consumer would say that the gain control
adjusts the picture’s brightness. In reality, gain is to brightness
as cubic zirconia is to a diamond. They look similar to an
untrained eye, but there are vast differences between them.
Adjusting the gain control changes the strength of the actual video signal.
On the other hand, when the brightness is adjusted, only the amount of
“white” in a picture is increased or decreased. In the realm of audio, gain is
synonymous with volume.
When shooting something that is dimly lit, the picture will be dark. In this
respect, the camera is no different from your eye. It is difficult, sometimes
impossible, for the human eye to see in the dark. A soldier on night
maneuvers, for example, absolutely must be able to see in the dark. In this
situation, night vision goggles are used. In recent years, news programs
have commonly shown images of night vision from war zones. However,
these images are not very clear. When a camera is shooting in the dark,
increasing the gain may artificially brighten the picture.
As the gain is increased, the resulting image becomes increasingly
grainy. This kind of picture is unusable in most professional productions. It
is recommended that for the vast majority of productions, the gain switch
never be moved from the “0” (zero) position. If an image is too dark, a light
source should be added.
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