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 low light level type of camera is the general camera of choice for most Navy
applications; it has higher reliability and greater operational range than
standard vidicon cameras.
6.2.1.3 Very Low Light Level. Specialized applications which have only
ambient lighting ranging from starlight upwards (0.0001 foot-candles) are
not often encountered. In military applications, they are limited generally
to exterior applications where "blackout" conditions are to be maintained at
a facility. For such conditions, very low light level cameras which use
Silicon Intensifier Target (SIT) or Intensified Silicon Intensifier Target
(ISIT) tubes should be considered. These cameras function generally the
same as other vidicons discussed above, except that the target materials are
extremely light sensitive. Because these cameras are very expensive (over
20 to 30 times the cost of a standard vidicon camera) and have a limited
tube life (6 months to one year), it is often more cost-effective to upgrade
lighting so that low light level cameras can be used. However, the Navy
security system designer may encounter applications where such cameras are
appropriate.
6.2.1.4 Solid State Cameras. These cameras are a relatively new
development. They use a solid state array such as a Charge Coupled Device
(CCD) to serve the purpose of the vidicon tube, and thereby eliminate it.
Since the other camera components have used solid state electronics for some
time, the vidicon tube has been the CCTV camera reliability "weak point" for
several years. Elimination of this vacuum tube increases reliability
dramatically as well as minimizing maintenance requirements for the camera's
interior components. At present, these cameras cost several times more than
a standard vidicon camera and generally provide the same light sensitivity
range. Although significantly more sensitive to the infrared and
near-infrared spectrum, as this type of camera production increases, its
small size and high reliability will make it the industry standard as cost
is reduced through increased production. Its use merits serious
consideration by the security system designer.
6.2.1.5 Camera Costs. The designated camera should be specified to provide
a usable picture under specific operating conditions. Performance is the
primary consideration for choosing closed-circuit television components.
Secondary to performance characteristics is the consideration of cost.
Table 10 outlines some basic data which are important to the design
engineering tasks.
6.2.2 Lenses. In order to "see" effectively, a CCTV camera requires an
eye" or lens. How well it can "see" depends upon proper lens selection.
How well an object can be seen is determined not only by the illumination or
sensitivity of the camera and contrast of the object against the scene
background, but also by how large the object is in relation to the entire
scene being viewed. Objects less than 1/10 of a degree in angle in a scene
cannot generally be identified by an observer. The camera lens determines
how large objects appear in a scene. Proper lens selection for each camera
is critical in CCTV system layout. Compromises in lens selection may be
possible for cost-effectiveness, but if a camera cannot see well, neither
will the
13.02-87
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