As with regular cameras, the lenses on CCTV surveillance equipment determines how wide an image is created and how much light is let in. Lenses are generally sold separately from cameras.
As with most CCTV surveillance equipment, lenses are fairly interchangeable between different brands and cameras, so you can usually reuses lenses from multiple sources. The lenses you purchase should match the format of your CCTV cameras, however: 1/4" lenses work best with 1/4" cameras. It is possible to use a larger format lens than the CCTV surveillance equipment calls for, but it is not recommended.
You also need to decide what type of lens your CCTV surveillance equipment requires. Fixed focal length lenses offer only one set field of view and are the least costly. To change the resulting image, you need to switch lenses. Variable focal length lenses and zoom lenses offer greater flexibility, allowing you to adjust your image’s field of view when you set the CCTV surveillance equipment up. Motorized zoom lenses, the most costly type available, give you the ability to control your cameras remotely. If you want to zoom out for general surveillance and in for detail when you spot suspicious activity, motorized zooms are the way to go.
If you will be using your CCTV surveillance equipment outdoors, look for a lens with an automatic iris. As in the human eye, the iris of a lens is what controls the amount of light coming in to the camera. Automatic irises can significantly improve performance for outdoor surveillance, where light levels vary considerably. However, you can save money and use a manual iris lens when the scene illumination never changes, for example in an illuminated store or office.