What are the lenses of security cameras
Most of our cameras always have two values at the end of the name, e.g. 3.6 mm / 85°. These two values are directly related and mean:
- 3.6 mm - indicates the value of the focal length, which determines the angle of view of the scene being captured.
- 85° - specifies the angle of view that the camera captures. Therefore, it is advisable, for example, to choose a camera with a larger angle of view for capturing larger areas and a camera with a smaller angle for capturing a gate at 30m.
Some cameras can be equipped with a so-called varifocal (VARIO) lens with a variable focal length (marked e.g. 2.8-12 mm / 95-28°). With such equipped cameras, you can manually or remotely (by motor) change the angle of view at your own discretion; this function may also be known by the general name ZOOM.
Table for indicative lens focus size
We work with the table by determining the distance of the subject from the camera in meters in the second row of the table. By scrolling down in each column, we find the expected dimensions of the square of the image to be captured.
Example: I need to have a close-up of the entrance gate to the building. I know the door is 5x2m and the camera is mounted on the house at a distance of 10m. I look up the 10m value and continue down the column. I find that the best value is V (height) 3.6m and W (width) 5.5m, which is best corresponds to a lens with a focal length of 8mm, which is an approximate angle of view of 40°.