Figure 14-8.Zoom lens.
You must be aware of two disadvantages of the
zoom servo. Although relatively quiet, some zoom servo
motors emit a humming noise that is picked up by the
camera-mounted microphone. Additionally, the motor
uses power provided by the camera battery.
FOCUS CONTROL. The focus control is
usually a rubber-covered ring on the zoom lens. To
operate it, you rotate the focus ring either clockwise or
counterclockwise while looking in the viewfinder to
determine if the picture is in focus.
Two methods of setting the focus on a zoom lens
are used. One, called zoom focus, is done by zooming
all the way in and setting the focus, then zooming out to
the desired focal length. Once this is done, everything in
the depth of field will remain in focus, including the
object focused on, provided the distance between it and
the camera does not change.
Another focusing method is called rack focus. This
is nothing more than your setting the focus on something
in the field of view. When you do this, only that object
and other objects at the same distance will remain in
focus as long as the distance between them and the
camera does not change.
You should rack focus when there is not enough
time to zoom focus. However, there are times when the
effects of a rack focus are desirable, such as when the
viewers attention is directed toward something in the
foreground and you want to lead him to another object.
You can do this by changing the focus to bring the other
object into sharp focus while the first object goes out of
As noted earlier, the camera pickup tube will
operate properly only within a certain range of light
intensity. If too much or too little light falls on the
pickup tube, the picture quality will suffer.
Since you will use the camera both indoors and
outdoors, you must compensate for extreme differences
in light levels. The lens diaphragm, or iris, is used to
control the amount of light that enters the lens and the
camera by enlarging or reducing the aperture. The
f/stops indicate the size of the lens (diaphragm) opening.