How to use spot metering, center focusing metering and partial metering in photography?

The photometry system of digital camera generally measures the intensity of reflected light of an object, which is called reflection photometry. The principle is simple. The camera automatically assumes that the reflectivity of the measured area is 18% gray (this value is obtained through a lot of research). When the reflectivity of the shot picture is higher than 18% gray scale, the camera thinks that the picture is overexposed and needs to reduce the exposure (reduce the aperture or speed up the shutter), otherwise the exposure is insufficient and needs to be increased. Let's take Nikon D3 100 as an example to see its metering mode.

Spot photometry

Spot metering, as the name implies, only measures one point, which is in the same position as the focus (actually it is only a small area, not a complete point). The advantage of this metering method is that it can measure a point that the photographer thinks is correct or the subject that is photographed correctly according to the photographer's preference, without interference from other light nearby. In other words, the camera only ensures that the exposure at this point is correct, regardless of whether the exposure at other places is accurate.

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

Central key photometry

The principle is the same as spot metering, except that it does not measure a point, but a relatively small area (generally about 10% in the center of the picture). Its advantage is that when shooting automatically, it is easier to get more real and close to reality metering, and there will be no exposure error caused by the wrong alignment of metering points. The disadvantage is that very small reference points cannot be measured correctly. In most cases, central focus metering is a very practical metering mode, but if the subject you need to shoot is no longer in the center of the picture, central focus metering is not applicable.

Suitable for shooting purposes: portrait photos, close-up photos and so on.

Matrix photometry

Matrix photometry and evaluation photometry are the same concepts. It divides the picture into several areas, and each area is measured separately. Then the camera processor summarizes the measured values of each area and calculates a final value by weight, thus measuring the whole picture. The advantage of this metering mode is that you can easily get a balanced picture, without local overexposure or underexposure of highlights, and the whole picture is balanced in light and shade. Its disadvantage is that it can't satisfy many situations, such as shadow, backlight and so on.

Suitable for shooting purposes: group photos, family photos and general scenery photos.

Sometimes the camera's metering system is not completely accurate. For example, when shooting a snow scene, the picture is always gray and the snow is not so white. In this case, another sharp weapon of exposure-exposure compensation will be used.

Accurate photometry is very important for obtaining photos with accurate exposure. In actual shooting, the shooting environment and objects are usually ever-changing, and digital SLR usually provides multiple exposure modes for different shooting objects to choose from. According to the actual shooting object and environment, choose the most suitable metering mode to obtain the most accurate exposure. Digital SLR cameras generally have the following commonly used metering methods: center average metering, center part metering, spot metering and evaluation metering.

1. central average measurement (or: central key average measurement, central key measurement)

This is the most widely used measurement mode and a variant of matrix measurement. The central average photometry mainly considers that the general photographer is used to putting the subject in the middle of the viewfinder, so the photometric data in the central area of the picture can be treated as "key", while the photometric data in the corner area can only be used for reference. Therefore, the sensory elements responsible for metering will organically separate the overall metering value of the camera, and the metering data in the central part accounts for the vast majority, while the metering data outside the center of the screen plays an auxiliary role in metering as a small proportion. After the processor of the camera weights and averages these two values, the photographed camera photometric data is obtained. In most shooting situations, central focus photometry is a very practical and widely used photometry mode, but it is not applicable if the subject is not shooting in the center of the picture or under backlight conditions.

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

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

Central part measurement and central average measurement are two different measurement methods. Center average photometry is a photometry method that focuses on the central area, supplemented by other areas, while the central part photometry only measures one area in the center of the picture, and the photometry range is about 3% ~ 12%. The central part metering mode is suitable for some scenes with complex light, and more accurate exposure is needed at this time. Photos of accurately exposed objects can be obtained by using central part photometry. Central part photometry can be applied to some special harsh shooting environments, which can ensure that the camera processor can calculate the exposure required for the main performance object part in the center of the picture. Partial photometry is to measure the light of a certain part of the picture. This method is most suitable when the contrast between the subject and the background is strong and the subject occupies a small proportion in the picture.

Suitable for shooting purposes: accurate metering is needed under certain conditions, and this mode is most suitable when the metering range is larger than spot metering, such as stage, performance, backlight and other scenes. .

Third, SPOT measurement (spot)

Although this metering mode can fully express the light reaction of the whole picture, it also has many shortcomings. For example, when the exposure of small-scale objects needs to be accurate, the central average photometry (central focus average photometry) is not so good, and even the central part photometry (partial metering) sometimes has a large range. In order to overcome these shortcomings, some manufacturers have developed this spot metering mode to avoid the influence of environmental light sources on the main metering under complex lighting conditions or backlight conditions; This is a fairly accurate photometric method, but it is not so easy for beginners to master it. How to distinguish a metering point has become a skill to be learned. The photos taken by the wrong metering point are either overexposed or underexposed, resulting in serious exposure errors. Spot metering used in digital camera macro shooting can make macro exposure more accurate. Spot metering is also a good weapon in portrait shooting, which can accurately expose parts of people (such as faces and even eyes). 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 purposes: stage photography, personal art photos, special story photos, etc.

Four. Evaluation photometry (or split photometry, matrix photometry and multi-region photometry)

This measurement method is a relatively new measurement technology, and multi-regional evaluation measurement is the most advanced intelligent measurement method at present. In this metering mode, the camera will divide the whole picture into multiple regions, then measure each region, and then synthesize the metering data of all regions to give a exposure value. This metering mode is suitable for landscape shooting because it can take care of every area of the picture.

Even people who are not familiar with photometry can generally get films with more accurate exposure in this way. It works best when shooting scenes with relatively positive light sources and uniform illumination, and has become the most commonly used metering method for many photographers and photographers.

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