How to measure light with SLR digital camera

Most digital cameras or traditional fool cameras have these metering methods: center average metering, center part metering, spot metering, multipoint metering and evaluation metering. These photometry methods can basically cope with all the current shooting, but in the photo studio and some professional occasions or advertising shooting, photographers still rely on the value of the exposure instrument to shoot. Let's take a look at these metering modes.

Central key average measurement (or simply: central average measurement)

Central average metering is the most widely used metering mode, and almost all camera manufacturers regard it as the default metering mode. Central average photometry mainly takes into account that general photographers are used to putting the subject, that is, things that need accurate exposure, in the middle of the viewfinder, so this part of the shooting content is the most important. 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. For example, Nikon's camera uses the central key to average metering, and the metering in the central part of Nikon's camera accounts for 75% of the total metering ratio (this ratio varies from brand to brand), and the metering data in other non-central parts gradually extend to the edge, accounting for 25%. In most shooting situations, central focus metering is a very practical and widely used metering mode, but it is not applicable if the subject you need to shoot is not in the center of the picture or under backlight conditions.

Central focus photometry is a traditional photometry method. Most camera metering algorithms pay attention to about 2/3 of the center of the picture, and consider the periphery. 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 purposes: personal travel photos, special scenery photos, etc.

Central part metering (or partial metering)

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. Using the central part to measure light, you can get photos with accurate exposure of the object. The central part photometry can be applied to some special harsh shooting environments, which can further ensure that the camera processor can calculate the exposure required for the main object part in the center of the picture. This mode is most suitable for scenes such as stage, performance and backlight, but due to the rise of split metering (matrix metering) mode, this mode is becoming less and less common in cameras. Canon, on the other hand, insists on central metering (partial metering). Up to the latest EOS30V film camera and EOS20D digital SLR camera, 9% area partial metering has been designed, which can make cameras without spot metering function reduce the influence of light on the subject when shooting pictures under some complicated light conditions.

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

Fixed point photometry

Although central average photometry (central focus average photometry) can fully express the light reaction of the whole picture, it also has many shortcomings. For example, when it is necessary to accurately expose small-scale objects, the center average photometry (center focus average photometry) is not so good, and even the center part photometry (partial photometry) 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; The range of spot metering takes a small area in the center of the viewfinder as the exposure reference point, and the metering area of most spot metering cameras is 1% to 3%, and the camera takes the light measured in this narrow area as the exposure basis. 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. Because of the skill of spot metering, it can also be used in macro shooting of digital cameras, which can make macro exposure more accurate. Therefore, people who like macro photography must study this metering method hard, and initially choose the middle small area in the picture as the metering reference point. Spot metering is also a good weapon in portrait shooting, which can accurately expose parts of people (such as faces and even eyes).

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 purposes: stage photography, personal art photos, special story photos, etc.

Multipoint photometry

Multi-point photometry is to achieve the best photographic effect through the brightness of different positions in the scene and the compensation of flash, which is especially suitable for shooting other light objects. First, the user should measure the background of the scene, usually the light source object, and then AE lock; Step 2, measure the backlight scene. Most professional or quasi-professional cameras will automatically analyze and use flash to fill the backlight object. Multi-point photometry can measure the brightness of several different points and calculate the final exposure according to the average value of these points. When shooting multiple objects, you can use multi-point metering, and even each object can be metered once. Therefore, multipoint photometry is suitable for special occasions such as high contrast, complex light environment and multiple subjects.

Evaluation photometry (or spectrophotometry)

Evaluation photometry (or spectral photometry) is a relatively new photometry technology, which has not appeared for more than 20 years. Nikon took the lead in developing this unique spectrophotometric method. The biggest difference between evaluation photometry (or separation photometry) and central key photometry is that evaluation photometry (or separation photometry) divides the framing picture into several photometry areas, and after each area is metered independently, the total exposure value is calculated by integral weighting. Initial evaluation photometry (or split photometry) is generally divided into eight parts. For example, Nikon divides the metering area into eight parts, and each part independently measures light through the camera's central processor and built-in data area. Cameras of Canon, Minolta and Pentax also have similar metering mode designs, but the difference is only the distribution of metering areas or different analysis algorithms. For example, the accuracy and rapidity of 2 1 area TTL photometry designed on Canon set-top computer depends not only on the hardware performance of the camera itself, but also on its processing ability and data analysis algorithm.

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 purposes: group photos, family photos, general scenery photos, etc.

The above introduces the principle of photometry and several common photometry methods, hoping to bring help to everyone in actual shooting. However, in actual shooting, the color of the object, various light sources and natural light and shadow will affect the photometric accuracy of the camera. When do you need exposure compensation? Positive compensation or negative compensation, these need you to judge according to the actual situation and experience. Take more films, watch more films and understand more. I hope everyone can take photos that they are satisfied with.