The accurate calculation formula of the focal length and the actual distance of the lens are monitored
Imaging scene imaging with the size of the display size of the object is contradictory, for example, with a camera to monitor the same parking lot, can choose short focal length lens to monitor the panoramic view of the parking lot vehicle pass in and out of the outside and see the entrances and exits, but could not see the car's license plate number (the car on the monitor screen only occupies a small area);
While the long focal length lens can see the license number of the car (the car takes up much of the screen), it can't monitor the whole parking lot.
Therefore, when it is necessary to monitor the panorama to see the local, it is generally considered that the electric two variable or electric three-variable lens should be considered. Of course, using high resolution cameras and monitors can also see the local details of the objects being monitored for an hour when the camera is selected
