In order to correctly select a lens and CCTV camera a number of considerations must first be taken into account.
Focal length is the measure of the zoom or angle the lens will view. A 2.8mm lens for example will view a wide area such as 90°. Viewing images at this angle however will not provide much detail as the subject is likely to be a small part of the image. A 50mm lens on the other hand provides a significant level of magnification or zoom meaning that a small area such as a face or number plate will take up much of the image. The result is a clear and identifiable image but without much coverage of the surrounding area.
On higher specification cameras the F-Stop or aperture setting must also be considered. A Small number eg. F1.0 represents a large lens aperture and will let a lot of light into the lens. This gives better low light performance but a much narrower depth of field meaning objects at only a specific distance will be in focus.
Every location must be carefully considered and the correct lens selected accordingly.
When we design a CCTV system each camera and lens combination will be tailored to the needs of that location.
Good Equipment and great advice thanks very much. 
