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 alarm station monitor. The discussion in this paragraph will be limited to
fixed focal length lenses. Variable focal length or "zoom" lenses will be
discussed in paragraph titled "Zoom Lenses."
Table 10
Camera Cost Comparison
Minimum
Initial [1]
Life [2] 10-Year Cost [3]
Imager Type Illumination
VIDICON
1 F/C
$300
6 mos.
$2,000
CCD
.3 F/C
$1200
10 yr.
$1,200
Low Light
.01 F/C
$800
1 yr.
$4,700
SIT
.001 F/C
$8000
6 mo.-1 yr.
$26,500
ISIT
.0001 F/C $10000
6 mo.-1 yr.
$37,000
1. Initial cost indicates only the camera and lenses; housings and
installation are not included.
2. The life cycle of the camera depends upon lighting conditions in the
viewed scene. Reflectance, proper lens operation, pan, tilt and zoom
functions, and periodic maintenance also influence the life cycle of the
camera.
3. The year cost equals purchase plus anticipated tube replacements.
6.2.2.1 Formats. The area seen through a lens is called the field of view
(FOV). Field of view depends upon the distance of the camera from the scene
and the scene size. Figure 32 depicts the relative FOV of various lens
types. How large an FOV a particular camera at a particular position can
have is limited by its format. The format is often the limiting factor in
camera lens selection. The FOV of a one-inch camera is about 1/3 larger
than that of a 2/3-inch camera with a lens of the same focal length. The
focal length is the length of the lens, generally expressed in millimeters.
Since the cost of the lens can approach the cost of the camera itself, this
illustrates why a one-inch format camera is usually preferred for outdoor
applications since a smaller (and less costly) lens can be used. A tradeoff
between camera format and cost and lens size and cost is an important part
of the design process. Lens speed, or f-stop, is the opening capacity of
the lens which determines how much light will be allowed to enter. The
f-stop is the focal length of the lens expressed as a function of its
diameter (f-stop x d = focal length). The more light, the better the camera
will see. The smaller the f-stop, the larger the lens diameter is for the
same focal length and the more light that passes through the lens. Since
most DoD and Navy applications involve cameras with an automatic iris, this
factor is less critical than where no automatic iris is used and is not
often a consideration for users of this design manual.
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