How to find the focal length

Solution of focal length:1/f =1/u+1/v (f is focal length, u is object distance and v is distance).

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. 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.

Optical clarity:

Focal length, also known as focal length, is a measure of light convergence or divergence in an optical system, which refers to the distance from the center of the lens to the focal point of light convergence. That is, the distance from the optical center of the lens to the imaging plane such as the backplane, CCD or CMOS 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.

A convex lens can image. Generally, when a convex lens is used as the lens of a camera, the clearest image formed by it will not fall on the focus, or the distance from the clearest image to the optical center (image distance) is generally not equal to the focal length, but slightly larger than the focal length. The specific distance is related to the distance between the subject and the lens (object distance). The greater the object distance, the smaller the image distance.

Approximate focal length:

For a thin lens in air, the focal length is the distance from the center of the lens to the main focus. For a converging lens (such as a convex lens), the focal length is positive, and a beam of parallel light will converge at one point. For divergent lenses (such as concave lenses), the focal length is negative, and parallel beams will spread out after passing through the lens.

Focal length in photography:

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.