Traditional Culture Encyclopedia - Photography major - How to measure light with grey card

How to measure light with grey card

Many people feel that it doesn't matter if they have too much exposure after using digital cameras, so they don't care much about exposure when shooting, and the gray card has been left out in the cold since then. In fact, although the exposure adjustment of digital photos is very convenient, some details of their overexposure cannot be revealed by lowering the brightness. Therefore, accurate exposure requires higher rather than lower digital photos. No matter whether it is a traditional camera or a digital camera, its photometric principle has not changed: reflective photometry, assuming that the subject is neutral gray with a reflectivity of 18%, and setting exposure data based on this standard. The camera doesn't know what you want to shoot, whether it's snow (reflectivity over 90%) or coal (reflectivity less than 10%), and the exposure is neutral gray of 18%. In the photos taken in this way, the snow is no longer white, the coal is no longer black, and it is gray without distinction. The function of the gray card is to provide the standard 18% gray scale, and the exposure value determined after photometry conforms to the original intention of photometry design. When gray turns gray, snow turns white and coal turns black. When the reflectivity of the object is close to the medium gray level, the exposure result of camera direct photometry (figure 1) is not obvious compared with that of gray card photometry (figure 2), and the difference between them is 1/3. Sometimes the exposure according to the subject (Figure 3) and the exposure measured by the gray card (Figure 4) are quite different (Figure 3 and Figure 4 are 4/3 different exposures). From the test results, the exposure accuracy of gray card photometry is obviously better. Photographers who pursue accurate exposure should never lose the good tradition of measuring light with gray cards and pursuing accurate exposure with digital cameras.