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Choosing the Correct Lens Download

Choosing the Correct Lens
 Lenses are the “eyes” of the camera.Choosing the correct lens for an cctv system is an important decision that is often misunderstood, even among industry professionals. Choosing a incorrect lens can result in poor camera performance and customer dissatisfaction.
CCD SIZE FIRST---1/3 CCD or 1/4 CCD
The first step to choosing a lens is to determine the CCD sensor size (420/480/600/650 TVL)of the camera you will be selecting a lens for. Choosing the wrong sized lens will cause the image too large for the sensor, resulting in a cropped image, or too small for the sensor which will cause the barrel of the lens to show in the image. Most CCD cameras(bangshi-camera) have a 1/3 inch, though many smaller ones utilize a 1/4 sensor. We have show the CCD size on website in all of our camera and lens specs, so make sure that the lens you are selecting has a size matching the camera specification. 


FOCAL LENGTH---3.6mm/4mm/6mm/8mm/12mm/.......
The most important factor in choosing a lens for your cctv system is the lens focal length, which is the distance (millimeters) from the optical center of the lens to the focal plane in the camera (the CCD). The focal length will determine the field of view, and is a crucial element for properly setting up your scene. 

Here has a formula to let you have a idea about the focal lenth: f = (d * s) / w, here  d = distance from object, s = sensor size, w = scene width and f is the focal length.

The sensor size should be change to millimeters first (3.6mm= 1/4 and 4.8 = 1/3).

For example, suppose you need to view a  5m wide area from 18m away with a 1/3 CCD: f = (18 * 4.8) / 5= 86.4/5 = 17.28mm, so a 16mm lens would do the trick.

Focal length has a direct relationship to field of view and depth of field. Longer focal lengths will make a narrower field of view and a shallower depth of field. Shorter focal lengths will make a wilder field of view, in opposite.