One of the problems with CCTV installations is that the wrong lens is chosen. This normally results in people being too small to recognise and depnding which camera you have you cannot electronically zoom in. To be able to recognise a person on a standard CCTV system they must be at least 50% height of screen.
To observe a person at 50% you can only view an area the width of two car park spaces (4.3m). The most popular lens sold to customers is a 1/3″ 3.6mm lens. This gives a wide angle view of 70-90% but can only provide facial recognition when someone is within 3.2 meters so if the camera is located at a height of 5m you are depending on an intruder bringing a ladder and climbing up in front of the Camera in order to be recognized. Generally a 3.6mm lens will only enable you to either observe or detect a person. (Please see below the different sizes of lenses and how they see)
Currently there is more versatile cameras on the market which will give you the capability to adjust the lens giving you a range for example from 2.8-12mm so you can actually zoom the camera in and set it at that point manually. Another advantage with the latest technology Digital cameras is that you can now actually magnify the picture and this will not change the Picture Quality. Recommended size Digital camera would be Megapixel quality but in my experience 2 megapixel is a great camera for this kind of option.
One of the main problems I see with CCTV Installations is that for some unknown reason they have installed the camera up to 20 meters high on a wall realistically do you think that they will get any facial shot being that high maybe they put it up that high to see peoples bald heads. As you can imagine the main offenders are usually unlicensed installers the main culprit being Electricians who seem to think they are automatic experts because they pull electrical cables.
Different kinds of lenses
Depending on what type of camera you are using there are different types of lenses that can be used but in general most cameras today have what is called Vari Focal lenses which means the lens is built in to the camera and can be adjusted manually to get the correct view that is needed. (Please see below an example of different kinds & size of lenses.)