One of the most important parts of any CCTV system is the lens/lenses, consideration should be given to each site dependent on changing light levels, the capabilities of the camera you are using and the object you wish to see. Once you have decided you should consider what type of lens best suits your application.

The most important points to consider when choosing a lens are the focal length and the iris type.

The focal length of a lens sets the angle of view that the camera can see. A short focal length lens has a wide angle of view.

Fixed focal-length lenses give a fixed angle of view. A vari-focal lens can be adjusted (within limits) to give exactly what is required.

The common focal lengths of fixed and vari-focal lenses and the approximate angles of view they give using 1/3” cameras are shown below:

Avoid using wide-angle lenses as they distort the picture so that vertical lines bend outwards. The amount of detail that can be seen from distant objects is low.

Manual iris lenses are best suited to indoor applications where light levels are more constant.

For outdoor applications, auto-iris lenses, either video-drive or direct-drive should be used.

back to top...

What is the difference between video drive and direct drive lenses?

Auto Iris lenses require a driving circuit to control the operation of the iris aperture under changing light conditions. The driving circuit can be located either in the camera or lens.

On a video drive lens the driving circuit is found within the lens itself. If, however you're using a direct drive or DC lens the circuit can be found within the camera. To control this function on a video drive lens, controls can be found on the lens and for a direct drive/DC lens on the camera. The majority of cameras will accept both types of auto-iris lenses with the operation of a switch. Some cameras will only accept either one or the other.


Can I put a CS-mount lens on a C-mount camera?

Cameras can be fitted with either a 'C-mount' or 'CS-mount' lens mounting. The difference between C and CS mount equipment is the distance between the flange of the lens and the focal plane of the lens (where the CCD sensor must be positioned). On C-mount lenses the flange back length is 17.5mm and on CS-mount lenses it is 12.5mm.

A C-mount lens may be used on a CS-mount camera with an adaptor ring but a CS-mount lens cannot be used on a C-mount camera, since correct focus cannot be acheived.

Some C-mount cameras do allow you to swap the whole mount from C to CS.


I have fitted my lens to my camera and cannot get it to focus. What am I doing wrong?

Ensure the format of the lens is the same format as the camera, for example if you have a 1/3" lens then you should have a 1/3" camera (this is not always the case but as a general rule you can put a higher format lens on a lower format camera but not the other way round). If you have the same format combination, then ensure you have removed the C/CS ring on the camera (this is a small ring fitted to the front of the camera , which is used to extend the distance between the lens and the camera when using a higher format lens to a lower format camera (e.g 1/2" and 1/3")) this is not required when using same format combinations.

back to top...