The relationship between the lens focal length and distance
a. The use place and view angle of camera lens:
1. from the perspective of more than 90 degrees, generally used in the elevator car, hall and other small sight angle places such as 2.8MM 2.5MM;
2, from the perspective of 5*5 meters for places 3.6MM 4MM in more than 60 degrees
3, from the perspective of 8-10 meters place for 6MM in more than 50 degrees
4, from the perspective of 10-18 meters place for 8MM in more than 40 degrees
5, from the perspective of 20-30 meters place for 12MM 16MM in more than 30 degrees
6, from the perspective of 30-50 meters place for 25MM in more than 20 degrees
Long focus lens:
7. the angle of view is within 20 degrees, the range of focal length from dozens of millimeters to hundreds of millimeters, for long distance monitoring
8. the lens has a variable focal range, which can be changed from the wide angle to the long focus, which is used for the area with large depth of field and wide range of view.
9. used for hidden monitoring. The smaller the focal length, the larger monitoring area, and the smaller the image objects. The larger the focal length, the smaller the area (narrower), and the larger the image objects.
b. Simple calculation method
visual distance equivalent to the focal length of the lens: view distance/2.4=focal length
lens *2.4 is the farthest distance to see: focal length*2.4=the view furthest distance