The lens that you select for your full body security cameras should match the format of the security camera. Examples of formats are 1/4”,  1/3”  and  1/2”. There are other formats but these are the most common available for most security cameras. These sizes refer to the diagonal distance across the CCD (Charged Couple Device). It is also important to remember, the larger the CCD format the greater the surface area, and therefore the more light that can be exposed through the lens. High sensitive cameras have a larger CCD and will be more affective in lower lit areas.

The purpose of the security camera lens is to produce a focused beam of light from the viewing scene onto the CCD of the camera. There are two forms of lenses available for the security camera. These are Manual Iris Lens and Auto Iris Lens. The Manual Iris Lens has a manually adjustable iris; this type of lens is best suited to indoor application where the light source is maintained. The Auto Iris Lens have either a video driven or dc driven iris, this type of lens is best suited in outdoor conditions where the light source will be varied. These types of lenses may also be used on indoor cameras. To control the amount of light that is passed through the lens onto the CCD, we use an iris. In the case of a manual iris when need to manually open or close the iris so to achieve the best contrast in the image. With the auto iris lens the opening and closing of the iris is controlled by a very small motor attached to the lens.

When choosing a lens for your security camera you need to consider the focal length required for the scene for which you have under surveillance. Positioning the camera is very important but sometimes you are unable to have the camera as close as you would like to the object that you wish to have under surveillance. With this in mind you are able to bring to subject closer to the camera simply by selecting the correct focal length lens. Let us say you have a camera that is mounted 50 meters away from a gateway. This gate way is our chock point, meaning all persons will enter through this gateway. Therefore, we would want a close shot of this gate way. We also need to consider the width of the scene; in this case, we want a width of 3 meters. The rule of thumb formula is as follows :-

Distance to the Scene in (mm) x 4 / Width of the Scene in (mm) = The Lens Focal Length

Therefore, in the above example we have the following :-

50000 x 4 / 3000 = 6.6 in this case you would fit a 6mm Lens to the camera.

Years ago all lenses had a fixed focal length, so you needed to calculate every lens when you quoted and you needed to ensure that you get the correct view the customers wants. If not you needed to keep trying other fixed lenses until you achieved the correct view. These days there are vari-focal lens, where you can manually adjust the focal length and achieve the best image possible. Therefore, in the above example, we would fit a 3.8 to 8.0mm vari-focal lens to the camera and we would be able to manually adjust the lens to achieve the exact 6.6mm that we required.

A simple fact with lenses is that the smaller the focal length number the wider the view will be. However, the wider the view is the further or smaller the subject will be in the shot. The opposite is true, the larger the focal length number the narrower the view is. Therefore, if you have an object that is far away from the camera you will need to fit a large focal length lens. There are many calculators out there to accurately tell you what lens to fit, but if you use the above rule of thumb you will be very close to achieving the correct camera view.

There are many other types of lenses available for security surveillance cameras, but we have only tried to explain some simple facts about lenses. In the hope that you may have a better understanding of what the lens is used for and maybe how to select the correct one.