The function of the camera lens is to collect light reflected from
the scene and focus it into an image onto the CCTV camera sensor.
Most CCTV applications use a fixed-focal-length lens, which, like
your eye's lens, covers a constant angular field of view. That is,
the fixed lens images a scene with constant magnification. A large
variety of CCTV camera lenses are available with different focal
lengths, which will provide different fields of view. Wide-angle,
medium-angle, or narrow-angle lenses produce different magnifications
and fields of view.
This handy field of view calculator will help you in determining
which lens is right for your application. Simply enter the distance
to the object, camera format, and focal length of the lens. Click
"Calculate" to see the field of view you can expect with that lens.
It also works in reverse. If you know the field of view you need,
enter it in and the distance to the object along with camera format
to find the focal length you will need to get the field of view