The role of surveillance cameras is to monitor the imaging area and convert it into electrical signals, according to specifications can be divided into 1/ 3 ", 1 / 2" and 2/ 3 " and other types of fixed installation and with two head whereas at the time of purchase of such security products to pay attention to their argument , here are some questions for the purchase of the camera parameters should be noted : A parameter of the photosensitive member Currently, the photosensitive element mainstream surveillance cameras using CCD element is actually a photoelectric conversion element . CMOS sensor and compared to the previous , CCD sensitivity is 3-10 times of CMOS , CCD chips can thus receive more light signal is converted to electrical signals by the video processing circuit filters, amplifies the video signal output is formed . The stronger the received optical signal , the amplitude of the video signal will be. Video signal to a monitor or TV's video input terminal can see the video image. Improve image clarity simply is to improve the photographic capabilities of the camera. Second, the parameters of the lens Aperture : Aperture is installed at the rear of the lens, the larger the aperture opening , the light passing through the lens , the greater , the higher the sharpness of the image ; aperture opening as small , the smaller the amount of light through the lens , the image clarity more low . Usually F ( flux ) to represent. F = focal length (f) / aperture . In the technical specifications of the camera , we can often see 6mm/F1.4 this parameter, which represents the focal length of the lens is 6mm, the luminous flux is 1.4 , then we can easily calculate the aperture of 4.29mm. In the same case where the focal distance f , F value is smaller , the larger the aperture , the luminous flux reaches the CCD chip is larger , the lens the better. FOV parameters: In engineering practice , we used horizontal field angle to reflect the shooting range of the screen. The focal length f , the smaller the viewing angle , the smaller the range of the screen is formed on the photosensitive member ; Conversely , the smaller the focal length f , the larger the field of view angle , the greater the range of the screen is formed on the photosensitive member . Focal length (f) parameters: the focal length is the distance between the lens and the photosensitive member by changing the focal length of the lens , the lens magnification can be varied to change the size of the captured image . When the distance between the object and the lens is very far when we can use the following formula expression : ≈ focal length magnification lens / object distance . Increase the focal length of the lens , the magnification increases , the vision can be closer to the range of the small screen , and the vision to see more clearly the details ; If you reduce the focal length of the lens magnification is reduced, expanded the scope of the screen can see more scenes. Surveillance cameras pixels and resolution than the computer 's video head higher but can not keep up professional digital camera or dv. Surveillance cameras just a single video capture device, it does not have the data storage function