What is the function of camera exposure meter? How to use it?

The main function of camera exposure meter is to automatically adjust the aperture or shutter time according to the intensity of external light (in fact, according to the illumination of the object surface), or to provide a basis for manual adjustment, so as to achieve the purpose of accurate exposure. For a traditional camera using film, it is necessary to adjust the sensitivity of exposure meter to be the same as that of film, and then use an exposure meter (or light metering point) to measure the subject (such as face). In general, the metering area of a camera divides the whole shooting area into several parts to measure light separately, and then calculates the average value (or weighted average value), and the metering value in the central area is the key point. Different cameras have different specific metering methods. The above mentioned exposure meters are attached to all cameras. The metering system of modern cameras is very developed. Why do many photographers use hand-held and independent exposure meters? Because (1) there are few cameras with perfect performance above medium film size, most cameras with large film size have no metering system. ⑵ Compared with the in-camera metering system, the hand-held exposure meter can have more sensitive and accurate metering performance, such as110 of the first aperture, which is more sensitive to low light. The measuring angle can also be very small, such as 1 degree, which is beyond the reach of the common cameras with "spot metering function" at present. ⑶ In some occasions, such as scenery, still life, products and model photography, it is not convenient to move the camera to measure light, but it is much easier to put the camera on a tripod and take an exposure meter to measure, think and judge. ⑷ The in-camera metering system can only measure reflected light, and the hand-held exposure meter can also measure incident light and flash. Exposure meter Reflected light exposure meters can be divided into two categories according to the different light being measured, namely, reflected light exposure meters and incident light exposure meters. The reflected light exposure meter is used to measure the reflected light of the scene and measure the brightness. Camera built-in exposure meters all belong to this category. Some hand-held exposure meters can only measure reflected light, but now most hand-held exposure meters can measure reflected light and incident light respectively. People who use the exposure meter must remember one of its basic principles: the result measured by the exposure meter is a medium gray tone on the final film or photo! The function of the exposure meter is: No matter whether the scene is bright or dark, it can ensure that the photographer can get images with equal brightness according to its instructions. The result is gray or medium gray with a reflectivity of 18%. Designers consider that the colors of most objects in the world belong to medium brightness, which can be used as a standard to adapt to most occasions. Only in this way can we ensure a visible image in most cases. So in a few cases, when the subject is pure black or pure white, it can't adapt and can't be restored. At this time, the photographer has to make adjustments to compensate. For example, if you shoot a large piece of white snow, you have to increase the exposure of 1-2, otherwise gray snow will appear in the photo. For another example, if you take a black camera, you have to reduce the exposure of 1-2, otherwise you will get a gray camera in the photo. If you don't understand this principle and the limitations of the exposure meter, you will screw things up in special occasions, which is especially important when using color reversal films. But the exposure adjustment range of color reversal film is smaller than that of negative film. When using a hand-held exposure meter, you must pay attention to its light receiving angle. Different exposure meters have different light receiving angles. Generally, the acceptance angle of an exposure meter is similar to that of a standard lens, ranging from 30 degrees to 50 degrees. Some reflected light exposure meters also have the problem of effective distance measurement. Some can measure the light near the object, while others are limited to a few centimeters away. When measuring distant scenes, if the receiving angle is too large to get readings, then the method of measuring substitutes with similar brightness can be adopted. You can also use the incident light exposure meter to get readings, and judge by experience, you can achieve correct exposure. Of course, the most convenient thing is to use a spot metering meter. Spotlight exposure meter Spotlight exposure meter is also a kind of reflected light exposure meter. Generally speaking, a spot light meter refers to an exposure meter with a measuring angle of 1 to 3 degrees. Spot photometers generally have a single function and no facilities for measuring incident light. However, some incident light exposure meters can greatly reduce the acceptance angle after adding accessories, such as measuring 5 degrees. The advantage of spot light meter is that it can measure the brightness of very small objects. In landscape photography, it can be used to measure the brightness of a scene in a calm place. 1 degree angle photometer can measure the transit of the moon. It can be used to measure the brightness of small parts in product photography. If optical fiber or miniature lamps are used for light distribution in advertising and product photography, only a point meter can be used for light measurement. Therefore, it is a common tool for photographers with strict exposure requirements and photographers who shoot color reversal films.