What is the meaning of EV in digital camera?

EV value is called exposure value, which reflects the synthesis of aperture size and shutter speed. The EV value is also related to the brightness of the scene and the sensitivity of the film. Generally speaking, the faster the film sensitivity, the brighter the subject and the larger the EV value, so it is necessary to use a small aperture and rapid exposure.

Exposure compensation means that the photographer corrects and adjusts the exposure "amount" determined by camera photometry, so as to get accurate exposure suitable for the correct performance of the subject. The exposure compensation is expressed by +3, +2,+1, 0,-1, -2, -3, etc. "+"means to increase the exposure based on the exposure determined by photometry, "-"means to decrease the exposure, and the corresponding number is the series (EV) of compensation exposure.

: numerical calculation

Calculation of EV value:

Assuming that the aperture value is set to f and the shutter speed is t, there is the following relationship:

EV = 3.322 log 10(f×f/T)

Every time the exposure value increases 1, the exposure will change by one step, that is, the exposure will be halved, for example, the exposure time or aperture area will be halved. This may cause confusion. The reason for the decrease, rather than the increase, is that the exposure value reflects the setting of camera shooting parameters, rather than the illumination of the film (mentioned in the next paragraph). The increase of exposure value corresponds to a faster shutter speed and a larger F value. Therefore, a bright environment or a higher sensitivity (commonly known as ISO) should correspond to a larger exposure value.

Like traditional cameras, the photometric exposure system of digital cameras has a very basic principle when processing images, which is to restore all subjects according to the neutral gray brightness of 18%. Therefore, in the photographic system of the camera, no matter what the original brightness of the object is, it should be displayed in a medium brightness tone at last. Therefore, in actual shooting, the photographer still needs to make corresponding judgments according to the complexity of the shooting scene, and only in this way can the ideal density and color reproduction be guaranteed.