What does it mean to set ISO when taking pictures?

Sensitive. O 50 ~ 100 is low sensitivity. In this part, you can get extremely smooth and delicate photos. As long as conditions permit, as long as you can take clear photos, try to use low sensitivity. For example, as long as the depth of field can be guaranteed, it is better to open the aperture one step than to improve the sensitivity one step. Ochre O 200 ~ 800 belongs to medium sensitivity. In this part, we need to seriously consider what this photo is used for and to what extent it should be enlarged. If noise can be accepted, the setting of medium sensitivity reduces the difficulty of shooting with hand-held camera, improves the safety factor of shooting in low illumination and improves the success rate. O 1600 ~ 6400 is of high sensitivity. The noise is obvious in this section. With this setting, the importance of the theme usually exceeds the quality of the image. After all, sometimes the shooting conditions are too bad, and it is better to take a slightly poor quality photo than not to take an image at all. The influence of sensitivity on photography is manifested in two aspects. One is speed. Higher sensitivity can get faster shutter speed and be easier to understand. The second is image quality. The lower the sensitivity, the finer the image quality, the higher the sensitivity and the higher the noise.