What is the focal length of the standard lens on the camera?

The focal length of a standard lens generally refers to 50 mm. At present, the nearest focal length of a general 50 mm lens is 0.45m, and the farthest is infinity.

According to the application classification:

A: Wide-angle lens: The viewing angle is over 90 degrees, the observation range is large, and the close-up image is distorted.

B: standard lens: the viewing angle is about 30 degrees, and it has a wide range of use.

C: telephoto lens: the viewing angle is within 20 degrees, and the focal length can reach tens or hundreds of millimeters.

D: zoom lens: the focal length of the lens can be changed continuously, and the focal length can be changed from wide angle to telephoto. The longer the focal length, the larger the imaging.

E: pinhole lens: used for hidden observation, often installed on the ceiling or wall.