What does the "EV" value of the camera mean?

EV is a quantity that reflects the degree of exposure. Initially defined as: when the sensitivity is ISO 100, the aperture coefficient is F 1, and the exposure time is 1 s, the exposure is defined as 0, and the exposure is reduced by one step (the shutter time is halved or the aperture is reduced by one step), and EV+1; Increase exposure by one step (double shutter time or increase aperture by one step), EV- 1.

If the metering system can't measure the light correctly, it is necessary to carry out +/-EV according to experience, and artificially interfere with the camera's automatic exposure system. So as to obtain more accurate exposure.

Extended data:

One of the purposes of displaying EV value on the light meter is to use some cameras with aperture and shutter speed linkage, which makes it easier to adjust the exposure. This camera adjusts the exposure according to the EV value. When choosing the aperture or shutter speed, the two can be linked to keep the exposure constant. The second purpose is to make the judgment simpler and clearer when it is used to measure the contrast of a scene.

Because as long as the difference between the bright and bright EV values is taken as the power of 2, its value is the light ratio. The EV value is also used to indicate the metering capability of the camera metering system. For automatic exposure, this photometric ability means the brightness range that can be used for automatic exposure.

Baidu encyclopedia -EV value