What does focal length mean? Pictures.

Definition of focal length: the distance from the main point of a lens or concave mirror to the main focus.

Focal length is a measure of light convergence or divergence in an optical system, which refers to the distance from the optical center of the lens to the focal point of light convergence when parallel light is incident. It is also the distance from the center of the lens to the imaging plane such as the backplane or CCD in the camera. An optical system with a short focal length has a better ability to collect light than an optical system with a long focal length. Simply put, the focal length is the distance from the focal point to the center of the mirror.

The lens of a camera is a set of lenses. When the light parallel to the main optical axis passes through the lens, the light converges to a point called the focal point, and the distance from the focal point to the center of the lens (that is, the optical center) is called the focal length. A lens with a fixed focal length, that is, a fixed focus lens; The lens whose focal length can be adjusted and changed is a zoom lens. (When a beam of light parallel to the main axis of the convex lens passes through the convex lens, it will converge to a point on the other side of the convex lens, which is called the focal point, and the distance from the focal point to the optical center of the convex lens is called the focal length of the convex lens. There is a focal point on each side of the convex lens. )

If you have seen "f =" in the English manual of the camera, then the number behind it is usually its focal length, that is, the focal length. For example, "f=8-24mm, 38- 1 15 mm (equivalent to 35mm)" means that the focal length of this camera is 8-24mm, and the oblique viewing angle is equivalent to 38- 1 15mm of the traditional 35mm camera. Generally speaking, the standard lens focal length of a 35mm camera is about 28-70mm, so if the focal length is higher than 70mm, it means that the telescopic effect is supported. If it is less than 28mm, it means that it has wide-angle shooting ability.