How to use 18% grey board

in the previous lesson, we mentioned that no matter what metering you aim at, exposure meter will "restore" it to 18% gray scale. Whether it's a dark coal cake or a white shirt. Professionals often use a gray board to measure light, and its gray level is also 18%. One side of this gray board is dyed gray, which can reflect 18% of the light shining on it. It can be bought in a professional photographic equipment store. We already know that all meters will be able to produce 18% gray as the exposure standard, so what will happen when we point exposure meter at the 18% gray board? The exposure value given by exposure meter should be able to produce a photo with the same tone as the 18% gray board. Then, the biggest advantage is that the light measured by exposure meter from the gray board is exactly the same as the light falling on the subject, no matter what type of exposure meter you use. Whether it is bright snow or water, dark coal or late at night, exposure meter will read 18% of the reflected light from the gray board. Then 18% gray on the gray board will be truly reproduced in the finished photo, and all other colors-darker or brighter-will also be truly reproduced in the printed image. All tones will completely reproduce their true colors in the photo. Therefore, whether shooting with color film or black and white film, it is equally reasonable to take the gray board reading as the exposure setting. This is a more accurate exposure method. If you have a high demand for exposure, we recommend that you don't be stingy with this money to buy a gray board. When we are faced with a difficult scene and need to measure light, it will help you solve a lot of trouble. Similarly, the use of gray board photometry also requires that the light irradiated on the gray board is basically the same as the light irradiated on the subject. When shooting still life or portrait, we usually put the gray board in the position of the subject, with the front facing the camera lens, so that both the gray board and the subject are under the same illumination intensity. For example, when the subject is standing in the shadow, don't measure the light of the gray board exposed to the sun. Similarly, when measuring light, the photographer should be careful not to block the light and ensure that the measured light is the same as the light when shooting.