Application and selection of measurement mode

Multi-area evaluation (or average metering) 3D matrix metering is the most common metering mode, and the camera metering system divides the picture into multiple areas.

Different cameras divide the area into different shapes and ways. For example, Nikon D 100 camera divides the object into 10 areas for metering. When the appropriate lens is used, the camera will use the 3D matrix to measure the light. When measuring light, the camera will make an evaluation according to the spatial distance of the object, and refer to the position of the subject and the contrast with the background to determine the weighted ratio of each area. After comprehensive measurement, the exposure value is determined, which is mainly suitable for the content with middle tone and relatively uniform brightness. This is a practical and scientific measurement method. Common subjects such as scenery photography, travel photography and family life photography can basically be exposed accurately by using this mode, including the use of flash. This mode is also a general camera program block (factory setting) mode, because it can provide more scientific exposure according to the overall balance of subject and background brightness, and it is a more convenient and reliable "fool" mode.

2. Central key metering mode

The metering area focuses on the center of the picture, and the rest is given average metering. When measuring light, the central sensing area varies from camera to camera, generally accounting for about one picture.

20-30% of the surface center. However, when Nikon D 1x and DI H measure light in this mode, 75% of the sensitivity is concentrated in the middle circle with a diameter of 8 mm.. Because the subject is in the central part in general photography, the central key metering mode with the subject as the focus and the background as the consideration has strong practicability. This mode is more suitable for shooting close-up flowers, busts, still life products and other subjects. The central key metering mode can also be used to shoot small-scale people's gatherings and travel photos, and it is also a practical metering method with a wide range of applications. If the subject is obviously biased to one side, or the brightness of the central part is obviously bright or dark in the whole picture, which is not representative, this mode should not be used. As shown in figure 1, the brightness of the surrounding background is quite uniform, and the face of the main character is in the middle, which is especially suitable for using this mode.

3. Spot metering mode

The metering area of spot metering is limited to a small position in the center of the picture. Generally, cameras with more than 4 million pixels have some metering functions, such as Sony DSC-S85, F7 17 and F828. In order to meet the extremely strict exposure requirements of professional photography, some digital SLR cameras have a very small spot metering angle, such as Nikon D 1x and D 1 H, and the metering range is concentrated in a circle of 4mm, which is equivalent to 2% of the whole picture. Photographers can choose a very narrow metering angle at will, and the selected "point" is quite accurate. This is mainly to meet the photographer's needs of exposure according to his own wishes in the environment of disparity between background and subject brightness. As shown in Figure 2, because the subject in the picture is small, the middle is black and the surrounding is dark background, it is more suitable to shoot with spot metering, and other metering modes may make mistakes.

4. Photometric mode of key autofocus areas

This is also a measurement method with high practical value. Not all cameras have this mode. It depends on the instructions. Its characteristic is that it is right.

At the same time, focusing completes metering, so for photographers who need to capture moments, they can get valuable opportunities when using them. In general photography activities, the focus chosen by the photographer is often the most important performance object, so the focus selection, exposure and other aspects are concentrated in this area, and the metering mode of the key AF area can be said to kill two birds with one stone. In addition to professional digital SLR cameras, some popular cameras, such as Nikon CO()LPIx series middle and high-end cameras 4300, 5000 and 5700, have similar functions. Of course, shooting moving objects requires agility, which depends on a lot of practice.

5. Requirements for using spot metering

Among all metering modes, the most difficult one is to use spot metering. "Only one point is not as good as the rest". From the empirical value, generally

Advocate junior photographers to use average metering mode, intermediate photographers to use center key metering mode, and advanced photographers to use spot metering mode. Because when using spot metering, the photographer must know which part is a typical l 8%% neutral gray part suitable for camera metering. If the brightness of the selected part is high, it is easy to be underexposed; If the brightness of the selected part is too low, it is easy to overexpose, so avoid self-defeating when using it.

6. Pay attention to the change of measurement position

Obviously, the choice of different metering methods will affect the final exposure effect. For some special objects, choices are made when shooting.

Photometric position and its change will also affect the exposure accuracy. After understanding the working modes of the above different metering modes, photographers should understand that the camera plays a key role in metering when working. If the photometric range is consistent with the exposure focus, you can shoot directly according to the instructions of the camera exposure value. If the main performance object is not in the center, you need to move the camera to re-compose and shoot after metering. The photographer must pay attention to whether it is consistent with the exposure data before moving, otherwise it will also affect the exposure accuracy, so the SLR camera has an "exposure lock" button to lock the photometric value. Photographers must be able to use this button flexibly and skillfully to avoid being in a hurry at critical moments.

7. The relationship between ordinary exposure mode and photometry

Both high-end digital SLR cameras and portable digital cameras have different automatic exposure modes, such as aperture priority and speed.

Degree of priority, program mode, manual mode, etc. It should be said that any exposure mode combined with different metering modes can get more accurate exposure. Some cameras have so-called scene modes, such as portrait mode, landscape mode, sports mode and so on. In fact, this is just another expression of aperture priority or speed priority mode. Using different scene modes only affects the depth of field or the blur degree of moving objects, and the exposure is the same. Because as long as the aperture or shutter speed changes slightly, the corresponding shutter speed or aperture will be automatically adjusted to compensate, and the exposure combination will change but the total exposure will not.

8. The relationship between manual gear and exposure

Generally, photographers rarely use the exposure manual when using digital cameras. In fact, many times, only the manual gear is used to control exposure.

Effective measures. It is assumed that the camera needs to be moved because of composition when shooting, and the original metering object will not be in the original position when exposed after moving. If an automatic transmission is used

At this time, the camera will "automatically" change the exposure, and finally "automatically" will lead to exposure errors. If a tripod is used to stabilize the camera and the "exposure lock" button cannot be manipulated by hand, then manual exposure should be adopted according to the exposure combination during photometry. Even if the camera prompts that the exposure is not accurate when shooting, it should be ignored, because the current exposure is not accurate, and it should be measured with photometric standard before re-composition. Of course, it doesn't matter if you don't use manual gear, but you should use exposure compensation to control the total exposure on the basis of photometry, so that the exposure obtained is more scientific. As shown in Figure 3, because the main body is on one side and the background is white, you must use manual occlusion to move the camera composition after spot metering.

In short, in photography practice, only photometry mode is available. Only the organic combination and flexible application of exposure methods can achieve ideal exposure effect. if

There are advanced cameras and correct photometry methods, but it is still difficult to get accurate exposure if the appropriate photometry object is not selected and the correct exposure method is not adopted.