How to correctly expose a SLR camera?

When we take pictures, if the subject is too bright, then the brighter parts of the picture will lose the performance of details because of too bright, so we say that such photos are overexposed; Similarly, when you take the subject too dark, the details of the dark part of the picture will be missing, and such photos will be underexposed. The following two photos are overexposed and underexposed. Such exposure is incorrect, and neither can be called a qualified photo. Elephant, the metering system of the camera is very powerful now. Generally speaking, there will be no obvious overexposure or underexposure when shooting with P, A and S files, but manual M file is different, because M file is purely manual, so novices often don't control it very well, and naturally they are more afraid of M file. Today, the author will focus on how to make the photo exposure accurate when using manual M file. The white flowers are photographed too brightly, and the details of the flowers are exposed after reducing the exposure. The sharp weapon of the M-file camera-exposure prompt Although all the parameters of the camera are set manually when we take pictures with the M-file camera, the camera, as our "good buddy", will still give us a kind reminder, which is the so-called exposure prompt. Where is this exposure tip? In fact, it is in a place that many people will ignore, that is, in the viewfinder. Detailed explanation of camera metering mode The metering system of digital camera generally measures the light intensity reflected by the subject. This metering method is called reflection metering. 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 metering, as its 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, and whether the exposure at other places is accurate. Suitable for shooting purposes: stage photography, personal art photos, special stories, etc. The principle of central focus photometry is the same as that of spot photometry, except that it measures a relatively small area (generally around 10% in the center of the picture) instead of a point. 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 is the same concept as evaluation photometry. 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. Another sharp weapon to control exposure-exposure compensation Let's continue the problem of shooting snow scenes just now. When the camera automatically measures light, the reason why the snow will feel gray is because the camera takes 18% gray as the standard when measuring light, that is to say, even if you take a picture of a blank sheet of paper, the paper you take is 18% "gray paper". In order to solve this problem, we have to "change" the camera's understanding of exposure standards, so exposure compensation appears. Exposure compensation is to consciously change the "appropriate" exposure parameters automatically calculated by the camera to make the photos brighter or darker. In this way, photographers can adjust the brightness of photos according to their own ideas and create unique visual effects. Generally speaking, the camera will change the aperture value or shutter speed to adjust the exposure value. Let's look at the samples first. All the samples were taken by setting the camera to the aperture priority automatic exposure mode and changing the brightness of the photos in stages by using the exposure compensation function. Generally speaking, in the case of camera aperture priority, increasing the exposure compensation value actually slows down the camera shutter speed, while decreasing the exposure compensation value actually speeds up the camera shutter speed. Exposure compensation is not a panacea, and underexposure is still possible in too dark environment. At this time, it is necessary to consider matching the flash or increasing the ISO sensitivity of the camera to improve the brightness of the picture. Summary: increasing exposure compensation is actually slowing down the shutter speed or opening the aperture, and the picture becomes brighter. Reducing the exposure compensation actually speeds up the shutter speed or narrows the aperture, and the picture becomes gloomy.