According to the application of civil buildings, the type of lens can be divided into:
First, wide-angle lens: angle of 90 degrees or more, generally used in the elevator car, the hall and other small viewing distance from the perspective of places;
Second, the standard lens: angle of about 30 degrees, generally used for walkways and community perimeter and other places;
Third, telephoto lens: angle of view within 20 degrees, the focal length range from tens of millimeters to hundreds of millimeters, for long-distance monitoring
Fourth, the zoom lens: the focal length of the lens variable, from wide to telephoto, for the depth of field, wide viewing angle of the region; (5) pinhole lens: for hidden monitoring.