What does focusing mean in photography? What's the use? thank you

Focusing is to adjust the focal length.

The function of focusing is to change the distance and the position of the distance through the camera focusing mechanism, so that the image of the object is clear. Generally, digital cameras have various focusing modes, namely, auto focus, manual focus and multiple focus modes. Early SLR cameras and paraxial cameras basically used manual focusing to complete the focusing operation.

Extended data:

Focusing is very important to ensure the clarity or clear range of the picture. The intersection of light rays is called the focal point, but the focal point is actually not a "point", but a surface on the screen, so the plane composed of all points that can clearly image the position is usually called the "focal plane", and the photographic lens can clearly record the objects on the focal plane. The farther away from the front and back of the focal plane, the more blurred the image is.

When the camera focuses, the general SLR camera is in a fixed focusing mode. Through the refraction principle of light, the light shot in the lens passes through, and then a phase difference is formed on the focusing module. At the same time, the progress of focusing is judged according to the focus. But relatively speaking, objects with a sense of depth from the focal plane may also be processed more clearly, which is the application of "depth of field".

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