How to control the correct exposure skills in photography skills?

Expert tip:

The three factors that affect the picture are aperture, shutter speed and ISO sensitivity, which influence and restrict each other.

The premise of learning exposure is normal exposure, and only in this way can we learn creative exposure more deeply.

In the case of overexposure or underexposure, we should be good at using exposure compensation to solve it. In addition, you can manually adjust the aperture, shutter speed and sensitivity.

1. Three factors that determine the exposure of photos

Learning exposure means learning three elements of exposure: shutter, aperture and sensitivity (ISO).

Shutter speed refers to the time from opening to closing of camera shutter, which is used to control the photosensitive time of CCD. Usually we express it in fractional form, such as 1/500, 1/250, etc. The faster the shutter speed, the less light passes through the lens. On the contrary, the faster the shutter speed is, the greater the difference in light input between adjacent shutter speeds is.

Aperture is a device used to control the amount of light entering the photosensitive surface of the fuselage through the lens. Aperture values F2.8, F8 and F 16 are the "coefficients" of the aperture. Simply put, the larger the f value, the smaller the aperture. For example, the aperture of F8 is smaller than that of F5.6, and the larger the aperture, the more light can be transmitted. On the contrary, the less light enters between adjacent holes.

ISO sensitivity, as its name implies, reflects the sensitivity of camera CCD to light. ISO 200 is higher than ISO 100. Sensitivity not only affects exposure, but also controls noise, which has an impact on image quality.

Then, after understanding the meaning and characteristics of each element, it is much easier to understand exposure. We call the process of shutter from opening to closing and CCD exposure from beginning to end exposure. In order to get a good and satisfactory photo, we need to properly combine the shutter, aperture and sensitivity. Let's give an example.

Aperture: F2 Shutter speed: 1/4000s Sensitivity: ISO 160 Focus: 50mm

Illustration belongs to the subject of portrait photography. Generally, we first use the aperture priority mode in this theme, and artificially choose a larger aperture to get a shallow depth of field effect, blur the background and highlight the main body of the character. After selecting the aperture of F2, the ISO sensitivity is set to 160 to ensure good imaging quality, and the bright area of a person's face is measured by spot metering mode, and the camera's metering system automatically gives the shutter speed of 1/4000s. In this way, the right aperture, the right ISO and enough shutter speed combined to take such a photo with accurate exposure.

Aperture can be used to control the length of depth of field. Under the same parameters, the scene with large aperture is deep and the depth of field with small aperture is long. So when we need to blur the background, we usually use a large aperture. On the contrary, if we want to get greater depth of field, we should use the smallest aperture possible.

When shooting a moving object, we want to freeze a certain moment, such as the moment when the athlete sprints to the finish line and the moment when the water splashes, so that we can get a clear picture. We still shoot moving objects, but we want to show the movement of the subject, so we can slow down the shutter speed appropriately and deliberately blur the picture, so it looks more dynamic. Another thing is that when we shoot the water, the slower shutter can get the silky effect of the water.

2. Normal exposure is the most basic exposure requirement.

Learning exposure is a gradual process. What beginners of photography should do at the beginning is to start with ordinary exposure, because only by learning the basic exposure and using the three elements of exposure and aesthetic sublimation flexibly can the creative exposure to be said later be brought to the extreme. It's like a child who is about to walk. Only through crawling practice can he transition to walking stage, which is a necessary process. Normal exposure is to choose the appropriate combination of aperture and shutter, which best conforms to the scene seen by human eyes and correctly restores the brightness level, contrast and color of the scene.

Aperture: F 1 1 shutter speed: 1/250s Sensitivity: ISO 100 Focus: 35mm.

The normal exposure picture is basically the same as the scene seen by human eyes. Gorgeous colors, blue sky and white clouds have a feeling of atmosphere.

Generally, it is enough to use the correct exposure value when shooting the beautiful scenery of a big scene. Normal exposure is used in most cases, such as portrait photography, still life photography and humanistic photography, and sometimes it needs to be adjusted according to the changes of subject and environment. Using exposure compensation is also an important means to effectively obtain correct exposure and rich levels and details of the picture.

3. Camera adjustment when the exposure is insufficient

Many times, the camera's metering system can't meet people's wishes, and there will be deviations more or less, which will affect the exposure of the picture.

For example, large areas of bright snow, we already know that the camera's metering system is based on gray with reflectivity of 18% through the study of metering principle, so if the exposure is carried out according to the metering value given by the camera, there will inevitably be underexposure. At this time, what we need to do is to increase exposure compensation to improve the whiteness of snow and show a sense of layering.

In addition, you can also deal with underexposed pictures by reducing shutter speed, increasing aperture and improving ISO sensitivity. It should be noted that the improvement of exposure compensation should not be excessive. Generally, cameras will have exposure compensation of +3EV and -3EV.

Aperture: F8 Shutter speed: 1/250s Sensitivity: ISO 100 Focus: 80mm

Because the aperture priority is selected, according to the scene light and the brightness of the subject, the exposure compensation of 0.7EV is increased, and the shutter speed is reduced from1160s to1100s, and the picture is exposed correctly.

White or light-colored subjects usually need to set certain exposure compensation. For example, white snow usually needs to add two exposure compensations, and white flowers need to add 1 block exposure compensation. If matrix photometry is selected when Nikon SLR cameras shoot with original G-type and D-type lenses, 3D color matrix photometry can be used, that is, the camera can detect the color of the subject and automatically set exposure parameters considering exposure compensation.

4. Camera adjustment when overexposed

In actual shooting, overexposure is often encountered. Of course, exposure compensation can also be used to reduce exposure and restore the correctly exposed picture. But sometimes even if the exposure compensation is reduced to -3EV, it can't completely compensate the overexposed picture. What should we do in this situation? It is suggested that beginners use M-stop to shoot, calmly increase shutter speed, reduce aperture or reduce ISO sensitivity to correct exposure.

Aperture: F8 Shutter speed: 1/250s Sensitivity: ISO 100 Focus: 50mm

After taking the first photo with the combination of aperture F8, shutter speed11000s and ISO sensitivity100, it was found that the picture was overexposed and details such as clouds and water surface had been lost. Instead of using underexposure compensation, set the dial to m, manually adjust the shutter speed, and set the shutter speed to 1/250s, and then try shooting several times to get this picture with accurate exposure.

Adjusting the aperture, shutter speed or controlling the ISO sensitivity of image quality depends on the content and theme of the picture to be displayed. As long as you remember to change any of these three parameters, the exposure will change accordingly. If it is gradual, then the exposure will follow a gradual change.

Surround exposure

Although the metering technology of digital cameras is improving day by day, there may still be metering deviation due to changing lighting conditions and shooting objects. In order to prevent important shooting pictures from being missed due to metering errors, digital SLR cameras usually have the function of automatic surround exposure, and usually take three photos: normal exposure, reduced exposure and increased exposure.

The method is to expose a photo according to the normal luminosity value first, and then reduce and increase the exposure on this basis. If you are not sure, you can set different bracketing increments to shoot, and you can adjust the exposure according to the level difference of 0.3EV, 0.7EV, 1EV, etc. The exposure of each photo is different, so as to ensure that there is always a photo that meets the photographer's exposure intention.

Aperture: F4 Shutter speed:11250s Sensitivity: ISO 100 Focus: 50mm.

By comparison, it can be seen that among the three photos taken by enclosed exposure, the photo taken without increasing EV value is the most reasonable exposure. Although three photos were taken continuously, the camera's automatic bracketing exposure function is helpful to obtain ideal exposure effect when pursuing accurate exposure of important photos.

Generally, SLR cameras are set with automatic surround exposure of plus or minus 0.7EV. In actual shooting, the camera will take one photo according to the normal metering value, one with -0.7EV exposure and one with +0.7EV exposure.

If continuous shooting is set, three photos will be taken by pressing the shutter at one time. If it is a single shot, you need to press the shutter three times to complete the photo shooting around the exposure combination. When the power is turned off or the flash is ready, the set automatic surround exposure value will be cancelled automatically.

6. Exposure compensation is an effective means to correct photometric error or creative exposure.

Almost all digital cameras have exposure compensation function, which can solve the problem of inaccurate metering in some specific shooting environments and create creative exposure pictures. Exposure compensation can usually be used in P, S, A and some creative modes. Its principle is to adjust the aperture size or shutter speed. For example, if exposure compensation is set in aperture priority mode, the camera will adjust the shutter speed to realize the exposure compensation set by the photographer and achieve the desired exposure effect.

Aperture: F8 Shutter speed: 1/500s Sensitivity: ISO 100 Focus: 150mm.

The silhouette under the backlight itself is a good subject for creative exposure. It abandons the light and dark levels and lines of the scene, and chooses to reflect the unique hue and atmosphere of the environment, showing the unique charm of photographic works. It is not enough to measure the light value of a reflected light to the area around the sun and focus on the grass in front of you. If the exposure compensation is reduced by 0.7, a particularly atmospheric picture will be obtained.

"exposure compensation" key

Exposure compensation is usually marked with+and-. The exposure compensation range of ordinary digital cameras is within 3 files, and high-end SLR cameras can reach 5 files. The exposure compensation can be adjusted according to 1/3EV, 1/2EV or 1EV. By reasonable use of exposure compensation, abnormal exposure effects can be produced, such as intentional underexposure or overexposure. In addition, exposure compensation is invalid under M-block, because under M-block, the parameters related to exposure are set by the photographer himself, and the camera metering system has actually been strongly sanctioned.