set or a direct view lens may also be used. The scenes can then be analyzed
for gaps in coverage, and format and lens tradeoffs can be accomplished.
Other considerations are:
a) Direct view lenses will invert the FOV image.
electronics revert it for viewing on a monitor.
b) One-inch format lenses may be used on 2/3-inch format cameras,
but not the reverse.
c) The focal length of a lens does not change, regardless of the
size of the camera vidicon (or solid state array).
d) A 25mm one-inch format lens has the same FOV as a 16mm 2/3-inch
e) The focal length of the lens has an inverse relationship to the
For a wide FOV, a short focal length is required and conversely.
f) Each camera layout is different, and a standard "system lens"
specification may not be possible, but if reasonable tradeoffs can be made,
it may be the most cost-effective approach.
g) As the lens focal length increases, the depth of field, or the
distance in the FOV where objects are in focus, decreases. If positive
identification of an object is required, this may be an important
6.2.3 Monitors. Monitors are the devices upon which the CCTV scene is
viewed. CCTV monitors generally come in standard sizes of 5, 9, 15, and 19
inches, measured diagonally across the picture. Taking into account the
primary requirement of an alarm station monitor to assess a scene only to
determine if an intruder is present, Table 12 provides a monitor size
selection guide based on documented human factors research. This research
says that given a standard TV picture of 525 horizontal lines and 350
vertical lines, a human will generally be able to see an object in a CCTV
display if it is from two to seven lines high in the picture. If the
requirement increases to positive identification, thus requiring more than
seven lines of picture, a larger monitor should be selected. Generally, for
access control monitoring, pan/tilt/zoom (PTZ) surveillance, and other
"close in" work, the 19-inch monitor is preferred. The 9-inch monitor is
used for most DoD security applications for alarm assessment. The
configuration of monitors is generally in stacked sets of two maximum per
alarm zone (other services use up to five in a horizontal row) and is a
matter of debate among human factor engineers. It is generally accepted,
however, that one operator can effectively handle data from no more than
eight monitors (four sets of two stacked vertically)