The aspect ratio of a standard CCTV picture is 4 units wide by 3 units high, typically complicated by being based on the diagonal measurement of the tube or sensor.
Camera lenses have the vertical and horizontal angles of view in the same proportions.
Many systems protecting a perimeter are looking along a long narrow field of view as illustrated in the diagram 1. This shows the view on a monitor in its normal orientation and with the camera mounted conventionally. The field of view will be determined by the vertical angle of the lens. It can be seen that there is a great deal of the screen showing areas not necessarily important in relation to the scene being monitored. This is because the orientation of the required scene is in a better relationship with that of the monitor.