Let's not talk about theoretical calculations, look at the picture:
The following content is also picked from the Internet, and is for monitoring camera parameters. In fact, the principle of an ordinary camera is the same; the distance is related to the field of view (when the focal length is unchanged, according to the above figure, it can be seen that the farther the distance is, the larger the corresponding viewing range. The larger the field of view), even a fixed-focus lens has a certain adjustable range.
The larger the value of the parameter selected by the surveillance camera lens, the farther and narrower the lens can be seen. On the contrary, the smaller the millimeter parameter selected by the lens, the smaller and wider the lens can be seen.
For example, if you want to select a 3.6-4MM lens within 10 meters, select a 6MM lens within 20 meters, and select 8MM within 30 meters.
For the lens, select a 12MM lens within 40 meters, and a 16MM lens within 50 meters, and calculate based on this (the lens is related to the use environment, everything is selected according to the actual situation).
The surveillance camera selects 1/3 of the lens to illustrate the surveillance angle:
①Monitoring camera lens 2.1MM small lens-monitoring angle 150 degrees;
②Monitoring camera lens 2.5MM small lens-monitoring angle 130 degrees;
③Monitoring camera lens 2.8MM small lens-monitoring angle 115 degrees;
④Monitoring camera lens 3.6MM small lens-monitoring angle 80-96 degrees;
⑤Monitoring camera lens 4MM-monitoring angle 78-80 degrees;
⑥Monitoring camera lens 6MM-monitoring angle 53-60 degrees;
⑦Monitoring camera lens 8MM-monitoring angle 40-45 degrees;
⑧ Surveillance camera lens 12MM- surveillance angle 23-30 degrees;
⑨Surveillance camera lens 16MM-surveillance angle 15-17 degrees;
Illustrate the relationship between focal length and monitoring angle:
①Monitoring camera lens 3.5-8MM-monitoring angle 96-45 degrees;
②Monitoring camera lens 6-15MM--monitoring angle 53-23 degrees;
③Monitoring camera lens 6-36MM-monitoring angle 53-10 degrees;
④Monitoring camera lens 8.5-51MM-monitoring angle 57-10 degrees;
⑤Monitoring camera lens 6-60MM-monitoring angle 53-6 degrees;
(Each manufacturer's lens angle is different, and there is a certain angle difference).