Dear photography lovers, who can help me explain "light ratio should not exceed 2.5EV exposure"

The EV value refers to the exposure, and its calculation method is the sum of the whole number of the EV value of the aperture plus the whole number of the EV value of the shutter.

You can check the EV value comparison table online. The same EV value means the same exposure. For example, if I shoot a cup, the aperture is 5.6, the shutter speed is 1/8 seconds, and the corresponding EV value is 8, then the corresponding aperture is 1 1, and the EV value of the shutter speed is 1/2 seconds, so both are 8. That is, the ratio of EV values. For example, in that cup, the light exposure (EV value) is 4 and the dark exposure (EV value) is 10, so the light ratio is 2.5. If we only discuss the aperture and shutter, we must have a certain sensitivity!