Why is the larger the aperture, the smaller the depth of field and the more blurred the background? What is the principle?

If the camera and lens are not moving at this time, move the point light source forward or backward a little. At this time, the image on the negative has become a fuzzy circle, not a point. The larger the aperture, the larger the blur circle, the smaller the aperture, and the thinner the cone of light passing through the lens, the smaller the blur circle.

For imaging, we feel that the smaller the blur circle, the clearer it is, so the clear range before and after opening the aperture is small, and the clear range before and after closing the aperture is large, which is the reason why the depth of field is different.

For example, a lens is used to focus on a luminous point, and countless rays from this luminous point pass through various points on the lens and finally converge on the substrate to form a point. Together, these lights are like a cone, like an umbrella that opens in front of the mirror and shrinks behind the mirror. The larger the aperture, the thicker the cone. No matter how big the aperture is, the image will be a clear point if the point light source is focused.

Extended data:

The amount of light entering the lens is controlled by changing the size of the hole. The larger the aperture, the more light enters the lens. Aperture values are usually expressed by f/ 1 and f/2. The larger the number, the smaller the aperture, and vice versa.

Under the condition of constant shutter speed, a proper aperture size can bring normal exposure. Excessive aperture will lead to overexposure, while too small aperture will lead to underexposure.

Aperture is not only used to adjust the exposure, but also to control the depth of field of the picture. The relationship between depth of field and aperture is that the larger the aperture, the shallower the depth of field, and the smaller the aperture, the deeper the depth of field. The smaller the aperture, the greater the corresponding value of f, for example, the aperture of f/22 is smaller than that of f/ 16.

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