How to Choose a Security Camera Lens
The lens you choose for your security camera will determine the field of view (width of the area monitored) and the detail your camera can record. Lenses mount to cameras with either a C mount or a CS mount; you must choose a lens that will fit your camera mount. Standard lenses come in three basic lengths which correspond to wide angle, normal angle, and telephoto. Generally, a 2.5 to 4-millimeter lens is a wide-angle lens, a 6-millimeter lens is a normal-angle lens, and a lens which is 12 millimeters and above is a telephoto lens.
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Instructions
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1
Measure from the camera to the far end of the location you would like to monitor and write down that figure as "Anticipated Target Distance" (D).
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2
Go to the location you want to monitor and measure the width of the area to be monitored and write that figure down as "Target Area Width" (W). For example, if you will be monitoring a doorway, measure from the camera to the doorway (step 1) then measure the width of the doorway (step 2).
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3
Look up the size of the camera CCD (charged couple device) and write down that as "CCD Size." (This is the size of the chip inside the camera that picks up the light; you can obtain this information from the camera manual or the website of the camera manufacturer.)
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4
Enter the above information in the lens calculator (see Resources) and press the calculate button.
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5
Select a lens which most closely matches the number the lens calculator displays.
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Tips & Warnings
If you are buying a camera and a lens, you may want to select your lens first and find a camera which will match the lens you want. You can purchase a variable length lens which will allow you to adjust the lens from wide angle to zoom. However, these lenses are expensive, are difficult to seal from moisture, and do not pick up light as well as fixed focal length lenses. You may be tempted to purchase a wide-angle lens to monitor a wider area than needed. However, this will cause all objects to appear smaller and will make it more difficult to see image details. When choosing a camera, the larger the CCD on a camera, the greater the detail in the image. If you must have very high quality images in an area which has strong backlighting, or an area which has varying lighting conditions, you may want to purchase a lens with a variable aperture. However, variable aperture lenses are much more expensive and require special cameras to control them. For standard security monitoring, a fixed aperture lens is usually sufficient.
