About photography: when shooting with a hand-held camera, can the shutter safety speed not be lower than the inverse value of the longest focal length of the lens?

LZ, what you said is wrong. It should not be less than the reciprocal of the focal length of the current lens.

For example, if you use a 50MM fixed-focus lens, the shutter speed should not be lower than 1/50.

For example, with a 70-200 zoom lens, the shutter cannot be lower than1/70 when using 70MM; When 125MM is used, it cannot be lower than1125, and so on. Otherwise, hand shaking will affect the clarity when shooting. Of course, many powerful people can still keep good definition when shooting with cameras in the dark environment where they can't see their fingers.