How does the exposure meter cooperate with the camera?

Experienced photographers can accurately estimate the exposure time under natural light when taking pictures. Even if there are some discrepancies, as long as the exposure is within the tolerance range of the film, qualified photos can be developed. For photographers who pursue high quality, it is difficult to meet the needs of accurate exposure by estimating exposure. For most photographers, it is often difficult to accurately predict unpredictable natural light, especially in special lighting conditions, such as morning and evening, night, indoors, under lights and so on. Therefore, it is necessary to use the exposure meter to determine the accurate exposure time of the subject.

I. Classification and characteristics of exposure meters

Exposure meter is an instrument that accurately measures the exposure required by the photographed object. According to whether it is self-contained or combined with camera, it can be divided into two categories: handheld exposure meter and built-in exposure meter.

① Hand-held exposure meter: it is self-contained, and it needs to be measured by hand when metering. Hand-held exposure meters can be divided into ordinary exposure meters (measuring the brightness of continuous light sources such as natural light and incandescent lamps, as shown in figure 1A) and flash exposure meters (measuring the brightness of instantaneous light sources such as flash lamps, as shown in figure 1B). In addition, hand-held exposure meters can be divided into incident exposure meters and reflective exposure meters according to different metering methods. The former is to measure the illuminance of the projected light, and the latter is to measure the brightness of the reflected light of the object. The exposure meter designed now has two functions: measuring reflected light and incident light. The metering part has a milky white cover. When the opalescent cover is not added, the brightness of reflected light is measured, and the incident illuminance is measured after the opalescent cover is added.

Flash exposure meter: There are two kinds. One is that there is a line connected to the flash, which can be triggered by pressing the button, and the brightness of the flash is measured at the same time, and the exposure combination value is fixed on the LCD screen. The other is that the flash has no wire connection. When in use, first open the exposure meter, and then manually trigger the flash to measure the brightness and exposure EV value of the flash.

Nowadays, the new hand-held exposure meter combines the brightness measurement function of continuous light source and flash light source into one. The same exposure meter can simultaneously measure the brightness of continuous light source and flash light source.

② Built-in exposure meter: This is a form of designing exposure meter inside the camera. Because the exposure meter is arranged in the camera, the trouble of carrying the exposure meter alone is avoided, and photometry can be carried out at the same time, which greatly improves the photometry efficiency. The exposure meter in the machine is a reflective exposure meter, which is divided into off-mirror metering (the exposure meter does not measure light through the lens) and in-mirror metering (the exposure meter measures light through the lens).

Modern cameras generally have built-in metering devices, which have advanced functions such as key average metering, spot metering and multipoint metering, and can fully meet the metering requirements under various lighting conditions.

Second, the use of reflective exposure meter

Reflective photometry is the most widely used photometry method, and the photometry in a single-lens reflex camera belongs to reflective photometry. In most cases, the effect of this measurement method is satisfactory. It is especially suitable for the following occasions:

(1) Under sunlight or shadow, the subject is evenly illuminated;

(2) subjects with a balanced proportion of dark parts and bright parts in the picture;

(3) There is little difference in brightness between the subject and the background;

(4) a small amount of sky scenery.

Because the reflective exposure meter measures the average brightness and regards the brightness value as the middle tone (neutral gray on the negative), the dark subject will be underexposed when measuring the picture of bright background and dark subject; When measuring dark background and bright subjects, the bright subjects will be overexposed. Therefore, when shooting these scenes, we need to take some correction methods:

(1) contains a large sky scene. When metering, the exposure meter should be slightly tilted to the ground, and then the camera lens should be adjusted to the original composition when shooting, and the exposure should be made by manual shift according to the metering value. Otherwise, exposure directly according to the original composition luminosity value will be underexposed.

② The illumination between the subject and the background is uneven. For example, if a person is in strong sunlight and the background is a large shadow, only by measuring the light near the subject can the correct exposure required by the subject be effectively determined. When shooting, return to the shooting position and expose according to the luminosity value of the protagonist.

③ Dark objects on bright background or bright objects on dark background. At this time, the light values of the subject and the background should be measured separately, and then the exposure should focus on the brightness value of the subject.

(4) The exposure of 1-2 should be increased if the hue is even and the color is dim, such as candlelight night scene; Bright scenes, such as snow scenes, need to reduce the exposure by 0.5- 1 level.

Thirdly, the use of event exposure instrument.

The incident exposure meter directly measures the illuminance of the light projected by the light source (Figure 2 is a schematic diagram of the use method), regardless of the reflective ability of the subject to the incident light. It means that the exposure to light-colored objects and dark-colored objects is the same, so that the tone of each light-colored object in the photo is brighter (because it reflects more light), and the tone of the dark-colored object in the photo is darker (because it reflects less light), so it can correctly reflect the light-dark relationship of the scene. In other words, it is more accurate to use the incident exposure meter than the reflection exposure meter. This is because the reflected light is greatly influenced by the environment and the reflectivity of the main body, and the metering error is large in some cases; The incident light is not affected by the above factors, so the photometric value is more objective and accurate. However, in many cases, such as shooting distant scenes, it is not convenient to measure the incident light near the subject, so it has certain limitations in use. Reflective exposure meters are generally suitable for the following occasions:

(1) Indoor themes under artificial light, such as portraits and still lives. ;

(2) Themes that require high level and texture, such as snow scenes, ice sculptures, black portraits, etc. ;

(3) The subject under backlight. Put an exposure meter at the position of the object, and determine the exposure by measuring the light receiving value on the front of the object, so as to obtain the correct exposure.

④ Small objects are small in size, so it is difficult to measure the reflected light of objects. It is convenient and accurate to measure incident light with incident exposure meter.