The relationship between the focal length and aperture of a camera

The so-called focus point of a camera generally refers to the autofocus point of the camera, and the layout of the focus point (such as straight lines, cross lines and rice lines) has a great relationship with the focusing performance of the camera. Aperture controls the amount of light entering the lens, not only the exposure but also the depth of field. It is not directly related to the focus of the camera.

However, there is still a certain indirect relationship between the two. For example, when using a lens with a small effective aperture (that is, a small aperture lens) or a magnifying glass, its effective autofocus point can only play a part because its maximum aperture is very small or will become very small. For example, the cross in the center of the picture or the cross (double cross) is effective for focusing, while the zigzag at the edge is ineffective for focusing because the light is too dark. So they are not completely unrelated.