An accurate calculation formula for monitoring the focal length and actual distance of the lens
So when you need to monitor the panorama to see the local, the general should consider the use of electric two variable or electric three variable lens. Of course, in the selected lens under the premise of the use of high-resolution cameras and monitors can be monitored objects in the smaller size can also see the local details.
While the use of long focal length lens can see the car's license number (the car occupies most of the area on the screen), but can not monitor the entire car park
The size of the imaging scene and the size of the imaging object are contradictory, for example, with the same camera to monitor the same parking lot, the choice of short focal length lens can be the entire parking lot to monitor and see the entrance Outside the vehicle out, but can not see the car's license number (the car in the monitor screen only occupies a small area)
