Why does SLR measure light?

The purpose of metering with SLR camera is to get the correct exposure. Only after proper exposure can we take another very clear photo. If the exposure is uncertain, taking pictures will reduce the picture quality.

Exposure is a Chinese character with pinyin of (bàoguāng) or (pê guā ng), which refers to the amount of light entering the lens and shining on the photosensitive element in the process of photography, which is jointly controlled by aperture, shutter and sensitivity. It also means that something is exposed or exposed. It means "sun", so it can be pronounced as pù, but this process is very fast, so it also means "fast", so the word "sun" can be pronounced as bà o.