surveillance picture

surveillance picture

Saturday, November 13, 2010

How to choose a CCTV camera lens?

When installing a CCTV camera system for your home or office, it is  very important cctv camera lensto choose the right lens for your CCTV camera. The camera’s lens determines how much the camera covers, how clearly you can see the area you’re monitoring, and how much light enters the camera. Here are a few things you must consider before buying a CCTV camera lens:
Focal Length
The focal length of a CCTV camera lens determines its angle of view and how far the camera can see measured in mm.The bigger the focal length, the narrower the field of view-that is, the more you zoom, the less area you see, and vice versa. Focal length of most CCTV camera lenses vary from 3.6mm to 16mm for fixed focal length lenses, to well over 70mm for zoom lenses.
Depth of Field
Depth of field is the amount of distance between the nearest and farthest objects that appear in  focus.A large depth of field means almost all objects  in the field of view are in focus and the vice versa-a small depth of field means only a small section of objects in the field of view are  in focus.The depth of field (DoF) of a CCTV camera lens is influenced by several factors. Wide angle lenses usually have a large depth of field than  telephoto lens, and a higher F stop setting as a rule  has a larger depth of field than a lower setting. The small depth of field is most apparent at night when the lens iris diaphragm is fully open and the depth of field is at its minimum.
The Iris of CCTV lenses
The Iris of a lens is another important detail to check before buying a CCTV camera lens. Most modern camera today use a type of  adjustable diaphragm known as an iris diaphragm, and often referred to simply as an iris. The Iris of a CCTV camera is either auto or manual. “Auto-iris’’ types of CCTV lenses  have a lead that connects to the camera itself, and provides the camera with the ability to let in more light in dark conditions, and less in bright conditions. This helps avoid the common problem of "sunrise glare", where the rising sun shines directly into the camera, completely blinding the camera's view. Auto-iris lenses come in Video or DC, and cameras generally support one format or the other.Those users who wish to use CCTV camera in an area (usually indoor areas)  that experiences infrequent changes in light, can use a manual iris lens, which is adjusted for light only by hand. 
Here are the things you must consider before selecting the CCTV lens. Always check the lens and camera before buying both.

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