Why does the shallow depth of field effect need a large aperture telephoto lens?

1, the depth of field is inversely proportional to the aperture, and the larger the aperture, the shallower the depth of field. Remember the law of photography.

2. The depth of field is inversely proportional to the focal length. The longer the focal length, the shallower the depth of field. Same as above, very easy to recite.

3. The f value is the aperture value. The larger f is, the smaller the aperture is, so the aperture of 50mmF 1.2 is large.

Remember the law of photography. If you must prove it, you can find a SLR, practice it yourself and prove it qualitatively.