How does a SLR camera measure light?

The camera needs to measure light before shooting, so how does the SLR camera measure light? Let me introduce you!

Why do you want to measure light?

The purpose of photometry is to get the correct exposure, and when the exposure is appropriate, you can get satisfactory photos. Otherwise, the photo may be underexposed or overexposed.

Although the current SLR camera can quickly find the right combination of aperture shutter and sensitivity, in the actual shooting process, the shooting environment and the opposite side are not static. As a user who pays attention to photo quality, he will choose the most suitable shutter and aperture according to the actual object to get the best exposure.

About the metering of SLR cameras, it is not easy to finish in a few words. Here are some materials to give a general introduction to the metering of SLR cameras. Let the newcomers have a general understanding.

Photometric mode of SLR camera

Most digital cameras have these four metering methods: central average metering, central part metering, spot metering and evaluation metering. As long as it is not a very professional occasion, these metering methods are enough to meet all shooting needs.

First, the central key average measurement (or simply: central average measurement)

Central focus photometry is a traditional photometry method. Most camera photometry algorithms pay attention to about 2/3 of the center of the picture, and consider the surrounding areas. For photographers who are used to using central focus metering, it is easier to control the effect by using this metering method than by using multi-zone evaluation metering method.

Suitable for shooting: personal travel photos, special scenery photos, etc.

Second, the central part of measurement (or: partial measurement)

Partial photometry is to measure the light of a certain part of the picture. When the contrast between the subject and the background is strong, and the proportion of the subject in the picture is not large, this metering method is the most suitable; In this case, partial metering is more accurate than the first and second metering methods, and unlike spot metering, because the metering point is too narrow to make mistakes, which requires some metering experience.

Suitable for shooting: under certain conditions, accurate metering is needed, and the metering range is larger than that of spot metering.

Third, SPOT measurement (spot)

Spot photometry can only accurately measure the light in a small area, and the brightness of the scenery outside the area has no influence on photometry, so the photometry accuracy is very high, and its main purpose is to measure the light in a specific small area in the distance. Mastering this photometry method requires the photographer to have a certain understanding of the point measurement characteristics of the camera used, know how to choose the photometry point with a reflectivity of about 18%, or make exposure compensation for the photometry point with a reflectivity higher or lower than 18% by experience. Spot testing is mainly used by professional photographers or people who know a lot about photography technology. Improper use of spot measurement method will add chaos.

Suitable for shooting: stage photography, personal art photos, special story photos, etc.

Fourth, evaluate photometry (or split photometry)

Multi-zone evaluation photometry is the most advanced intelligent photometry method at present, and it is a kind of judgment that simulates the uniform or uneven illumination that the human brain often encounters when shooting. Even people who are not familiar with photometry can generally get films with more accurate exposure in this way. This mode is more suitable for photos of big scenes, such as scenery and group photos. The effect is best when shooting scenes with relatively positive light sources and uniform illumination. At present, it has become the most commonly used metering method for many photographers and photographers.

Suitable for shooting: group photos, family photos, general scenery photos, etc.

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