What is exposure compensation? How to apply exposure compensation?

What is exposure compensation? Photography is actually a process in which a photographer uses his own photography technology to calculate the ambient light and capture the scene image through photographic equipment. This process is related to the aperture value of the device (controlling the luminous flux entering the camera per unit time), shutter speed (exposure time) and ISO (sensitivity to light). Nowadays, traditional devices and DC will calculate the ambient light through their own internal programs, and automatically adjust the aperture, shutter and even ISO value. However, in the Gao Fancha environment with complex light and strong contrast, the photos taken by P (programmed automatic exposure) blocks are often unsatisfactory and the effect is not the best. At this time, the photographer needs to manually adjust the exposure parameters of the equipment, that is, the exposure compensation EV (exposure value).

When the shooting environment is dark and it is necessary to increase the brightness, and the flash can't work, exposure compensation can be carried out to increase the exposure appropriately. When making exposure compensation, if the photo is too dark, the EV value should be increased. Every time the EV value increases, it is 1.0, which is equivalent to doubling the light input. If the photo is too bright, the EV value should be reduced. Every time the EV value is reduced, it is equivalent to doubling the amount of light entering. According to different cameras, the compensation interval can be adjusted in units of 1/2(0.5) or 1/3(0.3).

Without exposure compensation, the underexposure of lotus increased the exposure and improved the brightness of the flower. When the photographed white object looks gray or not white enough in the photo, the exposure should be increased. Simply put, it is "the whiter the better", which seems to run counter to the basic principles and habits of exposure, but it is not. This is because the camera's metering often focuses on the central subject, and the white subject will make the camera mistakenly think that the environment is bright, so it is underexposed, which is also the majority. The following are typical shooting scenes that need exposure compensation.

Forward salary:

1. When shooting text (black text on white paper)

2. Backlit portrait

3. Extremely bright scenery (such as snow) and highly reflective objects.

4. Negative compensation when the sky is clear:

1. Spotlight photos, especially when the background is dark.

2. When shooting text (white text on black paper)

3. Scenery with low reflection, such as taking photos of green or dark leaves.

Why exposure compensation? The human eye adjusts the pupil size by stabilizing the ambient light, and the middle gray level 18% is the average illumination value in our daily life scene. If this stable value is not reached within the range of adjusting the pupil of the human eye, the ability of the human eye to correctly judge and identify the environment will be reduced. Photographic equipment is based on this principle to calculate ambient light. The camera completes the measurement of light after half pressing the shutter, and automatically adjusts the aperture, shutter and ISO value after program calculation to wait for the next operation. To put it simply: the bright and dark objects in the photos taken by "program automatic exposure" can show a medium gray tone of 18%. Like human eyes, the camera can't correctly show the ambient light beyond this value on the negative /CCD. Several methods of exposure compensation There are many methods of exposure compensation and adjustment. Generally, there are external light compensation such as flash lamp, photographic lamp and reflector. Adjustment of aperture value and compensation of luminous flux parameters for exposure time. Strictly speaking, the above compensation methods should be classified as the concept of "light compensation or exposure control". There is also the adjustment and compensation of EV. The compensation of external light by flash lamp is hard in the absence of other supplementary light sources, which often leaves obvious shadows on the background of the subject, and at the same time makes the highly reflective part of the subject lose its sense of hierarchy and has serious distortion, so it is rarely used. Photographic lighting can create a good shooting effect, but it is often limited to the studio due to the limitations of conditions. Reflective plates with soft light and supplementary light effect are widely used in portrait photography in small scenes, mostly for supplementary light on the main face, and their limitations are self-evident. The adjustment of aperture and shutter luminous flux parameters is often due to the need to consider the influence of depth of field and moving objects in the shooting process, which will have a feeling of being stretched in practical application. For the popular equipment, the most common method is to adjust EV to achieve the purpose of exposure compensation.

Ke Mei α-7D exposure compensation turntable, yellow label 1/3EV, white label 1/2EV, most consumer digital cameras have an adjustment range of 2.0EV, and the DC of high-end products can reach 3.0EV. One of the indicators to test a DC is its manual adjustment function, and the adjustment accuracy is also an important factor in EV adjustment, generally 0.3 or 0.5. The smaller the grade difference, the more satisfying the photographer's creative intention. Correct use of exposure compensation function For beginners, exposure compensation is generally used for still life and scene shooting. This situation is suitable for you to adjust the parameters calmly, shoot many films with different compensation values, and choose the best works from them. Correctly adjust the EV value: use EV+ in typical underexposed scenes (objects have many bright areas, such as water surface, snow scene, sunrise and sunset scene, etc.). ), and use EV- in typical overexposed scenes (dark areas with many objects, such as dense forests, shadows and close-ups of black objects, etc.). ). Simply put, it is "white plus black minus, bright plus dark minus". It should be noted that the aperture/shutter parameters of the camera will change when the EV value is adjusted, regardless of whether the DC is in the P file or the S/A file: when the EV is adjusted in the P file, the aperture and shutter of the camera will be automatically adjusted; The fixed aperture under the adjustment of block A and EV will change the shutter speed; When the shutter is fixed under the S-stop and the EV adjustment is linked, the aperture size will change. However, these changes of aperture and shutter will not affect the exposure compensation effect after final imaging. For the special effects shot in DC M block, the aperture and shutter speed can be adjusted independently, and after setting the aperture/shutter configuration, an EV compensation parameter will be automatically given according to the calculation of ambient light when completing DC metering, which cannot be adjusted manually. However, we can still use the "parameter overflow" beyond the compensation extreme value to achieve the creative purpose: that is, we can use the part beyond the EV compensation value that the digital camera can't achieve to achieve the creative purpose. At this time, the EV value appears red on the LCD screen (parameter overflow).