Solve the relationship between depth of field and focal length

Focal length: the longer the focal length, the smaller the depth of field and depth of field; The shorter the focal length, the greater the depth of field.

Changing the focal length mainly changes the ratio of image distance to object distance. The longer the focal length, the greater the influence of object distance on the change of image distance, and the larger the dispersion circle formed. The depth of field is approximately proportional to the square of the focusing distance L, that is, the focusing distance has greater influence on the depth of field than the aperture, and the closer the subject is to the camera, the shorter the depth of field.

Depth of field is also related to object distance. The smaller the object distance, the smaller the depth of field; The greater the object distance, the greater the depth of field. The depth of field is also related to the aperture size. The longer the focal length, the greater the nearest focal length, the shorter the focal length and the smaller the nearest focal length.

Extended data:

Chinese expression of depth of field formula;

Depth of field = (2× the diameter of the diffusion circle× the square of lens focal length× the aperture value× the square of focal length)/(the fourth power of lens focal length-the square of the diameter of the diffusion circle× the square of aperture value× the square of focal length)

Depth of field on the back = (diameter of diffusion circle × aperture value × square of focusing distance)/(square of lens focal length-diameter of diffusion circle × aperture value × focusing distance)

Foreground depth = (Diffuse circle diameter× aperture value× focal length square)/(Lens focal length square+Diffuse circle diameter× aperture value× focal length)

References:

Baidu encyclopedia-depth of field