How to get accurate exposure in photography

In the process of photography learning, photography techniques such as composition and color can be learned by observing excellent works and pondering carefully, but it is difficult to understand this technique from the surface of works only through accurate exposure.

The accuracy of exposure is the most important link in the process of photography creation. It requires beginners not only to observe excellent works, but also to constantly use and try in practice. The initial exposure of mistakes is a normal phenomenon, and only by accumulating experience in constant mistakes can we gradually realize it.

Of course, those photographers who pour out their chests will explain in detail what kind of scenery they aim at, how to measure light and how to control exposure, so that their works have charming light and shade changes. Don't miss these explanations, they are the essence of their decades of photography experience.

First, in photography creation, there is no right only accurate exposure.

Snow scene? Hengfu photo

Canon EOS 5D Mark II camera

Lens focal length 300mm aperture f/ 14 speed 1/4s ISO 100.

Bright white snow and strong reflection on the water surface are both factors that affect the automatic exposure accuracy of the camera. At the same time, the author needs to think carefully when pursuing the gray scale of the picture and the subtle transition and expression in a small range. In the reflection of the water surface, the branches and leaves of shrubs with medium gray tones are not much different from the reflection of bright sky and snow, but they are also delicate enough. A little gray-black tone of the resting waterfowl plays a finishing touch in the picture.

In photographic physics, exposure refers to the process of physical changes caused by light received by photosensitive materials. For traditional film cameras, photosensitive materials refer to film, while for digital SLR cameras, it is the process of CMOS photosensitive elements and recording data.

For ordinary photographers, every photo will be "correctly" exposed by the camera, regardless of the automatic exposure of the camera. But is the "correct" exposure result all we want?

Snow scene? Hengfu photo

Canon? EOS 5D？ Mark II camera

Lens focal length 400mm aperture f/5.6 speed 1/400s ISO 100

Compared with Snow Scene 4, the author immersed this work in a dark tone. The "accurate" exposure in his mind is beyond the automation of the camera. The trunk and hidden space in the dark tone form a subtle contrast with the branches covered with snow, which is clear and not abrupt, adding a mysterious and profound feeling.

For creative photographers, "there is no correct exposure, only accurate exposure". In photography creation, exposure is not only a completely automatic physical process, but also a photographer's thinking and creative process, which is controlled by people. That is, referring to the automatic exposure result of the camera, according to the photographer's creativity, actively control the exposure of a certain work.

Secondly, the automatic exposure process and the gray board with reflectivity of 18%.

Since accurate exposure is artificially adjusted on the basis of camera automatic exposure, we must first understand the process of automatic exposure. Automatic exposure is an exposure control amount calculated by comparing the photometric data obtained by the camera with the gray board with reflectivity of 18%, that is, the combination of shutter speed and aperture. What is the concept of grey board with reflectivity of 18%? Why should it be defined as a standard?

Mcburney's works

Canon EOS 5D camera lens focal length 50mm aperture f/5.6 speed1125 iso100.

The concept of scenery reflectivity

First of all, the reflectivity of an object is the ratio of its ability to reflect light according to the structure and material of the scene surface. We use percentages to calculate and measure the reflectivity of different scenes. The reflectivity makes them look bright and dark. The reflectivity of metallic silver polished surface is 92%, which looks extremely bright. The reflectivity of carbon black is about 2%, so it looks very black. In daily scenes, the reflectivity of red brick walls is 20%, showing a medium gray brightness; The newly fallen snow surface has a reflectivity of about 75% and looks bright and dazzling. How can we make them all behave appropriately in a photo?

Mcburney's works

Canon EOS 5D camera

Lens focal length 60mm aperture f/5.6 speed1125ISO100.

Using grey board to measure light, the intensity of the irradiated light can be directly measured, which is not affected by the environment. For example, these two works use white and medium gray backgrounds respectively. If in-machine metering is used, the exposure effect will be inconsistent, and corresponding exposure compensation is needed. However, the accurate exposure combination can be directly obtained by directly placing the gray board near the model as the photometric object. Careful observation of the brightness of the person's skin is completely consistent.

Neutral gray board with reflectivity of 18%

Therefore, the standard organization determines the intermediate reflectivity as the benchmark: the performance of neutral extremely bright scenes (100%) and extremely dark scenes (2%) under the same illumination. Determine the neutral point according to the approximate multiple relation, as follows:100%-50%-25%-12.5%-6.5%-3.2%-1.6%. Look! 12.5% is the initial intermediate reflectivity and intermediate brightness. In order to meet the practical and convenient needs of photography, Kodak, a tycoon in photography, produced a neutral gray board with a reflectivity of 18%, which was finally determined as the contrast standard of automatic exposure.

Third, the original exposure value EV.

The word exposure comes from English Exposure Values, abbreviated as EV, which is a measure of the exposure of gray board standard with reduced reflectivity of 18% under different brightness conditions. It is controlled by shutter speed and aperture.

That is, we often say that under a certain sensitivity ISO, the exposure combination can make a scene with a certain brightness sensitive. It is the logarithmic sum of exposure time and the logarithmic sum of aperture value. To simplify the calculation, we have listed the above table to help you understand.

Li Yu's Smoked Works

Canon? EOS 50D？ camera

Lens focal length 17mm aperture f/ 1 1.

Speed 1/500 sec ISO 100

The determination of EV in exposure value is a scientific and rigorous process, and using a camera for photometry is one of the most accurate photometry methods. Usually, the combination of EV113 of f/8 and 025 s in clear weather is only suitable for low-altitude plain areas, while the light is stronger in high-altitude areas, so the shutter speed is increased by 2 levels, reaching 1/500 s. At this time, our shooting experience in sunny days is not accurate. So in the process of shooting, we must rely on the dual strength of technology and experience.

When the sensitivity is ISO 100, the aperture f/ 1 and the exposure time is 1s, the exposure EV value is 0; When the aperture and exposure time change, the EV value changes accordingly. We can calculate the specific exposure value in the table below.

Ordinary cloth products

Nikon D80

Lens focal length 80mm aperture f/3.5 speed 1/250s ISO 100.

When shooting portraits in backlight, if you don't use reflector or flash to make up the light, you must consider the positive exposure compensation of 1EV, that is, increase the exposure of 1, so as to ensure the normal exposure of the face of the person in backlight and show the eyes and demeanor of the person. If you follow the camera's automatic exposure, it will cause the failure of "little black face", remember to remember.

Our common sunny days, aperture f/8, exposure time1125 seconds, EV value 13 are all calculated in this way. The result of automatic exposure is the exposure combination of aperture and shutter speed displayed in the camera frame according to this table.

Fourthly, different exposure combinations under the same EV value.

Under different lighting conditions, exposure value EV is different, so it has different shutter speed and aperture. But under the same lighting conditions, exposure value EV is the same, so does it fix a single shutter speed and aperture composition? Let's take a look at the EV value table above!

When the EV value is 13, we can find different exposure combinations: aperture × shutter speed.

f/ 16× 1/30s = f/ 1 1/60s = f/8× 1/ 125s = f/5.6× 1/250 = f/4× 1/500s = f/2.8× 1/ 125s

Li Yu's Smoked Works

Canon EOS 50D camera

Lens focal length 1 10mm aperture f/1/speed 1/20s ISO200.

When shooting landscape works, it is usually necessary to apply small aperture to pursue the maximum clear range of the scene, that is, the effect of large depth of field. For such works, the exposure combination determined by the camera is usually f/4 and1160s. Photographers need to adjust the exposure combination to the aperture of f/ 1 1 and the speed of 1/20s according to the reciprocity law of exposure, so as to ensure the clear presentation of houses and mountains.

So we get that under the same lighting conditions, we can use different exposure combinations and get the same brightness results. In fact, this is the theorem of reciprocity law obtained by German chemist Benson when studying illumination, that is, exposure is the product of exposure time (shutter speed) and light source intensity (aperture size).

Works of Liu Lu 8330

Nikon D200? camera

Lens focal length 200mm aperture f/3.5 speed11250siso100.

Shutter speed is the most important determinant when shooting works of moving scenery such as birds. Usually, the shutter speed cannot be lower than11250 s, so as to freeze its moving posture. For such works, the exposure combination determined by the camera is usually f/5.6 and 1/300s. Photographers need to adjust the exposure combination to the aperture f/3.5 and the speed11250s according to the reciprocal law of exposure to capture the moment when seagulls catch food.

The law of reciprocity plays an important role in photography. Creators can shoot different effects with different shutter speeds and aperture combinations on the basis of the same exposure. For example, if the EV value is 13 on a sunny day, the camera will automatically set the exposure combination to the aperture f/1,the shutter speed1125s, and the flower photographer can shift the exposure combination to f/2.8 and1/kloc. The landscape photographer will use the aperture f/22 and shutter speed 1/30s to increase the depth of field of the picture, resulting in a clear effect from close-up to distant view.

Mastering the law of reciprocity of exposure will make your photography level go up a big step, from being controlled by the camera's automatic function to actively controlling the camera.

Fifth, actively control exposure compensation

After such a big circle, we finally figured out the automatic exposure principle of the camera, and also understood the reason why we used to take satisfactory photos with a fool camera-the scientific and technological principle contained in the camera can make us get "correct" exposure.

However, in the process of photography creation, when we shoot some special scenes, the "correct" automatic exposure of the camera is wrong-when we shoot white snow fields, the photos come out as dark gray snow fields; When we shoot a tiny dancer on a dark stage, the stage is bright, but the dancer is extremely bright, blurred into a shining angel, and the photo is overexposed. The camera is broken?

E888LP project

Canon? EOS 5D Mark II? camera

Lens focal length 200mm aperture f/2 speed 1/640s ISO500

A small bright light source on the runway illuminates the female model as the protagonist, and other scenes are dark. In order to take care of the dark parts, the automatic exposure of the camera will increase the exposure and make the dark parts brighter. But this is not the author's creative needs, so we should take the initiative to attack, suppress the secret level and highlight the subject. The author makes good use of the contrast between light and shade and reality, and forms a deep effect in his works.

Of course not, the camera is not broken, but it is set to restore all the scenery to 18% gray, and whether it is bright white snow or dark stage, it will become gray, gray stage or gray coal. At this time, it is necessary to take the initiative to attack and command the camera again: "Now it is white snow, so we should increase the exposure and make positive exposure compensation." Exposure compensation is a kind of control behavior that we must artificially increase or decrease exposure when we encounter special subjects in photography creation. These special themes include shooting scenes that are too bright or too dark, backlighting or lighting conditions with large light ratio, or giving low-key or high-key image effects to works.