The metering principle of the camera

The metering system of digital cameras generally measures the brightness of light reflected back from the subject, which is also called reflective metering. Now I will introduce to you the photometry principle of measuring camera, I hope it can help you!

The metering principle of the camera

The metering principle of the camera (digital and various film) is not complicated. The most important thing is that we must understand that the camera’s metering system (or What is the measurement basis of a light meter? In layman's terms, when a camera measures the light of a scene, how does it "think" about what it sees?

Remember: During the metering process, all cameras will default to gray with a reflectivity of 18% for all objects they "see" (the professional term for photography is "mid-level gray" ), and use this as the basis for photometry. In other words, in the "eye" of the camera, all subjects are gray, and the purpose of exposure is to correctly restore this gray.

Why this special 18% gray? Because 18% gray is the same color tone as the average reflected light of human skin (16~20%), and people are the most common objects we photograph. (The reflectivity of other objects, such as silver is 96%, white drawing paper is 75%, pure black is 3%, etc.)

When the light meter is working, it depends on whether the reflectivity of the subject is 18%. If the reflectance is 18%, then the measured value is very accurate. If exposed at this value, the color and tone of the subject will be truly restored. Therefore, it is good for our skin and normal For colorful scenery, this kind of exposure based on gray tone as the restoration standard is very accurate.

If the reflectivity of the subject is not 18%, then the value measured by the camera metering system will be inaccurate. If you directly expose according to this value, the tone and color of the picture will be distorted: like shooting The camera will also restore the vast white snowfields and dark coal fields as gray, and meter and focus directly on them, which will often produce gray snow and coal.

Tips: In digital photography, several tips for reasonable light metering:

① To shoot snow scenes, you can first half-press the shutter with your hand, that is, to Measure the light on your own skin, and then press the shutter on the snow you want to photograph. Then the snow will be white. In the same way, when taking a portrait of a person wearing black clothes, you should meter the face first and then compose the shot. )

② When photographing bright objects, you should use an aperture 1 to 2 stops higher than the index recommended by the light meter, and for dark objects, the exposure should be appropriately reduced.

③ Taking photos in a sunny season will produce a great contrast in the photos, so it is necessary to meter the bright and dark parts of the scene separately, and take photos with the average exposure index of the two.

Big tip: Remember some of the following substances. Their reflection values ??are close to 18%, which may be very useful for everyone when shooting under complex conditions:

① Grass (mown) Grass!), but note that it is not dark green, particularly green or yellow grass;

　②Most light green leaves or plant leaves;

　③Some, but not all tree trunks ;

　④Old, repaired asphalt roads and concrete (this is very useful);

　⑤Lumber that has been placed for a long time and has not been oiled;

⑥Red /Brown bricks, including cement walls;

　⑦Dry leaves.