Difference between 4 mm and 6 mm cameras

The focal length of home monitoring is 6mm. The difference between 4mm and 6mm cameras lies in different viewing angles and different monitoring distances.

1, different views:

4mm focal length and 79 field of view; The focal length is 6mm and the field of view angle is 49.

2. Different monitoring distances:

4mm focal length, monitoring distance of about 6 meters; The focal length is 6mm, and the monitoring distance is about 10m.

The application of focal length in photography;

When the camera lens is adjusted to infinity, it is actually a nominal focal length. In design, the distance between the main plane of the lens and the negative or imaging sensor is adjusted to the length of the focal length, and then the distant object can form a clear image on the negative or sensor.

The focal length is usually marked in millimeters (mm), but you can still see that some old lenses are marked in centimeters (cm) or inches. The size of the field of view depends on the ratio of lens focal length to film size. Because the most popular specification now is 35mm, the field of view of the lens is often marked according to this specification.