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 6.2.2.2 Field of View Layout. This is a critical step in CCTV subsystem
design. Without a proper FOV layout, the wrong equipment will be specified,
perhaps preventing the alarm station monitor from correctly assessing an
alarm, causing a costly system failure, and leading to an expensive
retrofit. The field of view to be covered by a particular camera should
first be measured. Then the correct lens should be selected based upon what
format camera is to be used. Table 11 provides a useful guide to lens
selection. Many lens manufacturers provide this data on a small pocket
slide rule accompanying their advertising literature. If only one-inch
format camera data is available, the FOV dimensions required may be
multiplied by 1.43 and the result found on the same table to determine the
size lens required for a 2/3-inch format camera. If the lens has been
selected for a one-inch camera, the focal length multiplied by 0.7 will give
the correct size lens for a 2/3-inch format camera. The 25mm lens is
considered the industry standard. It is defined as having a magnification
(M) of one. To determine the M of a lens, divide the lens focal length by
25 (e.g., a 75mm lens has an M of 3). The FOV of each camera and lens
should be carefully laid out on accurate drawings of the facility. These
should be confirmed by trial measurements in the field, if possible, ideally
using a portable camera set at the selected lens focal length and a video
tape recorder (VTR). A single camera/monitor
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