SECURITY SYSTEMS & SOLUTIONS
A lens is an optical device which bends light, focusing it on onto a image sensor to create a distinct, visible image.
How a Lens Works ?
The camera lens is a remarkable invention that attempts to duplicate the operation of the human eye. Just like the eye, the lens sees an image, focuses on it, and transmits colors, sharpness, and brightness through the lens to the sensor. Like our memory, the image sensor records the image for processing. When light strikes the front surface of the lens and passes through the glass element, the light rays bend and change direction when they enter glass. By using various glass shapes, lenses are able to channel the light in a specific direction. The focus controls this direction so that the light rays converge on one point, exactly where the image sensor is located in the camera.
The field of view (FOV) is based on the camera & lens. Wide angle lenses are suitable for most applications due to their ability to view a large area. A 4mm wide angle lens will be able to view an area 20’ high x 26’ wide at 21’ away. As an example, a 15’ x 15’ room is shown in the diagram below. Observe that 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 (such as above a cash register or over a greater distance), an 8 or 12mm may be desired. The same camera (above) at 21’ away with a 8mm lens will have a 10’ vertical x 13’ horizontal FOV. At 21’ with a 12mm lens, the FOV will be approx 6’ vertical x 9’ horizontal. Increasing the focal length of the lens decreases the perceived distance to the viewing area. See the FOV diagram below for approximate views with different focal length lenses.
3.6mm Fixed Lens – 72° View, 6mm Fixed Lens – 43° View, 8 mm Fixed lens -33º, 12mm Fixed Lens – 22° View, 16mm Fixed Lens – 19° View