What of the following allows security personnel to change the field of view of a CCTV lens to different angles and distances?

A.
Depth of field

B.
Manual iris

C.
Zoom

D.
Illumination

Explanation:
C: Zoom lenses provide flexibility by allowing the viewer to change the field of view to different angles and distances. The security personnel usually have a
remote-control component integrated within the centralized CCTV monitoring area that allows them to move the cameras, and zoom in and out on objects as
needed. When both wide scenes and closeup captures are needed, a zoom lens is best. This type of lens allows the focal length to change from wide angle to
telephoto while maintaining the focus of the image.
A is incorrect because depth of field refers to the portion of the environment that is in focus when shown on the CCTV monitor. The depth of field varies
depending upon the size of the lens opening, the distance of the object being focused on, and the focal length of the lens. The depth of field increases as the size
of the lens opening decreases, the subject distance increases, or the focal length of the lens decreases. So, if you want to cover a large area and not focus on
specific items, it is best to use a wide-angle lens and a small lens opening.
B is incorrect because an iris controls the amount of light that enters the lens. Manual iris lenses have a ring around the CCTV lens that can be manually turned
and controlled. A lens with a manual iris would be used in areas that have fixed lighting, since the iris cannot self-adjust to changes of light. For example, it may be
used in hospital hallways that are always lit.
D is incorrect because illumination refers to the intensity of light present in an environment. Different CCTV camera and lens products have specific illumination
requirements to ensure the best quality images possible. The illumination requirements are usually represented in the lux value, which is a metric used to
represent illumination strengths. The illumination can be measured using a light meter. The intensity of light is measured and represented in measurement units of
lux or footcandles. (The conversion between the two is one footcandle = 10.76 lux.) The illumination measurement is not something that can be accurately
provided by the vendor of a light bulb, because the environment can directly affect the illumination. This is why illumination strengths are most effectively measured
where the light source is implemented.