Lenses for network video cameras

Lens elements

A lens (or a lens assembly) on a network video camera performs several functions, including:

  • Defining the field of view, which in turn determines the how much of a scene can be seen in the image.
  • Controlling the amount of light reaching the image sensor so that the image is correctly exposed.
  • Focusing the image, by adjusting elements within the lens assembly itself, or by changing the distance between the lens assembly and the image sensor.

Lens types

Depending on the application, there are several types of lens to choose from:

  • Fixed lens: the focal length is fixed and provides a single field of view.
  • Varifocal lens: offers a range of focal lengths, and thus different fields of view. The field of view can be manually adjusted, although this also requires the lens to be refocused.
  • Zoom lens (also known as telephoto lens): similar to varifocal lenses in that they offer multiple fields of view, but here there is no need to refocus if the field of view is changed. Focus is maintained within a range of focal lengths.
A fixed focal lens (left), a varifocal lens (center) and a zoom lens (right).

Figure 1: A fixed focal lens (left), a varifocal lens (center) and a zoom lens (right).