In photography, what is the concept of 18 degree gray?

Two meanings.

The first layer of photogrammetry takes the reflectivity of 18% as the exposure reference value. (Because the commonly used photometric system of the camera takes the gray scale of 18 as the reference value, when the measured value of a pure black subject or a pure white subject is compared with the gray scale of 18, there will be a great error, resulting in overexposure or underexposure of the actual photometric value! ) refer to the website 1: /index.php? Showtopic=34067 This website has real pictures. You will understand it better if you look at them.

How to measure light? way

First of all, ensure that the light irradiated on the gray board is basically the same as the light irradiated on the subject. Both should have the same strength. For example, when the subject is standing in the shade, don't measure the light of the gray board exposed to the sun. If the subject is in the shade, it is necessary to measure the light of the gray board in the same shade.

Secondly, we may notice that if the photographer's hand is projected on the corner of the gray board. If our subject is exposed to the sun at this time, we must make sure that we are not measuring this shadow.

Thirdly, the gray board we bought in the store is about 8 inches × 10 inch, which is too big to put in the camera bag. Don't be shy, cut it in half or four pieces, and just put a small piece in the camera bag. The size of the gray board is enough as long as it can measure light at close range when shooting.

Fourth, read the gray board data with a hand-held exposure meter. We can also use the camera's built-in exposure meter to read the gray board, and the effect is the same.

Fifth, even if our camera has automatic exposure function, we can use gray board. If our camera can lock the exposure reading, we can do the following:

First, read the gray board data at close range and press the exposure lock.

Then, while locking this exposure in place, aim the camera at the scene you want to shoot and take the next picture. If the light illuminating the scene is the same as the light read from the gray board, then the exposure is correct.

Sixth, we may notice that there are similarities between the gray board reading and the incident light reading. In fact, they should provide exactly the same recommended exposure, and they all measure the light that illuminates the subject. When we measure the incident light, the white plastic cover on the light meter allows 18% of the light to pass through, which is exactly the same as measuring the reflected light on the gray board. The gray board reflects 18% of the light shining on it. If the lighting is the same, then the two readings should be the same.

Also, if you use the hand-held exposure meter "Shiguang 608 with a white ball", there is no need to use 18 gray board, because that is equivalent to 18 gray board!

The second layer is the digital age (only applicable to digital cameras). It is used to customize the white parallelism of the camera. The specific settings of each camera are different. The settings of the same brand are generally the same. Not much to say here. You can explain your camera model, and I can tell you how to listen.