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Television Production & Broadcast Journalism
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and back, the image is magnifi ed or shrinks accordingly. This particular
moving piece of glass within the lens assembly is called the zoom lens.
This individual zoom lens is the focal point, or optical center, of the zoom
lens assembly. The image is inverted wherever the zoom lens is positioned,
within the range of the lens assembly, Figure 3-14.
As stated earlier, both the individual glass discs and the
tube-shaped piece of equipment that houses the glass
discs are called “lenses.” The same is true of the zoom lens
assembly and the specific zoom lens within the assembly;
they are both referred to as “zoom lens.” Pay attention to the context to
determine which one is meant.
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Focal length is the distance (measured in millimeters) from the focal
point of the lens assembly to the back of the lens assembly, Figure 3-15.
zoom lens: The particular
piece of glass within the
lens assembly that moves
forward and back, magnifying
or shrinking the image
accordingly. This individual
lens is the focal point, or
optical center, of the zoom
lens assembly.
focal length: The distance
(measured in millimeters)
from the focal point of the lens
assembly to the back of the
lens assembly.
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Focal point changes
Figure 3-14. The
individual zoom lens slides
forward and backward
within the zoom lens
assembly. The focal point
is located wherever the
zoom lens is positioned.
20 mm
7.8 mm
120 mm
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Figure 3-15. The focal
length is the distance (in
millimeters) between the
back of the lens assembly
and the focal point.