What does focal length f mean?

The focal length f is an important parameter of an optical lens, which indicates the distance between the position where the lens focuses light and the central plane of the lens. If the focal length f is short, the lens focuses the light to a farther position, and if the focal length f is long, the light is focused to a closer position. The larger the focal length f, the smaller the image becomes, and the objects close to the lens lose focus faster.

For digital cameras and SLR cameras, focal length is a parameter mainly used to describe the lens. Lens with different focal lengths have different shooting effects. Ultra-wide-angle shooting has a large field of vision, which is very suitable for shooting buildings and landscapes, while telephoto lens can enlarge the target and is suitable for long-distance shooting, such as sports events. The focal length will also affect the depth of field and clarity of the photo. When shooting with short focal length, the field of vision is wide, the scenery is deep and easy to shake; A longer focal length will pay more attention to the details of the subject and distinguish the face and expression of the person in the photo more clearly.

Focal length can be used not only in digital cameras and SLR cameras, but also to describe the parameters of wide-angle cameras and video cameras. In a camera, the focal length is usually expressed as a numerical value. Generally, the value of f is between 30. 1 and 30 1. These numbers represent that the length of a lens is 1 mm, which is equivalent to 35 mm film (0/2 inch away from the object/kloc-0). In addition, the focal length of a wide-angle lens usually varies greatly. In the super wide-angle lens, you will find that the focal length is about 8 mm, while in the standard wide-angle lens, the focal length can be between 28-50 mm