The lens field of view angle of the captured scene is a very important parameter. The lens field of view angle changes with the lens focal length and the size of the camera specification (the change relationship is as described above). The focal length of the lens covering the scene can be calculated by the following formula:

(1) f = u · D / U

(2) f = h · D / H

f: Lens focal length, u: actual height of the scene, H: actual width of the scene, D: measured distance from the lens to the scene, u: image height, H: image width

For example:

When 1 / 2 "lens is selected, the image size is u = 4.8mm, H = 6.4mm. The distance from the lens to the scene is d = 3500mm, and the actual height of the scene is u = 2500mm (the actual width of the scene can be calculated by the following formula, H = 1.333 · u, which is determined by the CCD film of the camera viewfinder).

By substituting the above parameters into formula (1), f = 4.8 · 3500 / 2500 = 6.72mm can be obtained, so 6mm fixed focus lens can be selected.

It is used to determine the viewing angle observed by the camera. According to different needs, lenses with different focal lengths are used to obtain the best viewing angle.