Field of View
Field of view (FOV) is a measure of how large an area a CCTV camera is capable of viewing. The FOV is based on the camera and lens. For example, a 15' x 15' room is shown in the diagram below. The 4mm lens (green arrows) allows better wide-angle viewing coverage than the 12mm lens (red arrows).
In applications where a closer view is needed (e.g., above a cash register or over a great distance), an 8mm or 12mm lens may be a better choice. The same camera at a distance of 21 feet using an 8mm lens will have a 10' vertical and 13' horizontal FOV. At 21 feet with a 12mm lens, the FOV will be approximately 6' vertical and 9' horizontal.
Increasing the lens' focal length decreases the perceived distance to the viewing area, but also decreases the area that the camera is able to view. See the FOV diagram below for approximate views with different focal length lenses.
The FOV can be calculated as follows:
W = width of object
H = height of object
w = width of image sensor format
1/2 format = 6.4mm, 1/3 format = 4.8mm, 1/4 format = 3.6mm
h = height of format
1/2 format = 4.8mm, 1/3 format = 3.6mm, 1/4 format = 2.7mm
f = focal length
L = distance to object.
EXAMPLE: You would like the full image of a 6-foot (1.8m) tall person to appear on a CCTV monitor. The person is approximately 20 feet (6m) away from the security camera. The camera uses a 1/3-inch format CCD sensor.
h = 3.6mm
H = 1.8m = 1800mm
L = 6m = 6000mm
You'll need a 12mm lens for the best results for this application.