In the photography of SLR cameras, its parameters remain unchanged, and the higher the ISO, the darker the picture. I hope the prawns can explain it in detail, thank you ~ ~ ~

ISO stands for the sensitivity of photosensitive elements to light. The lower the value, the less sensitive it is to light. Therefore, under the same aperture shutter, the picture brightness of ISO800 will be greater than ISO 100. However, because the photosensitive element receives too much light, it will affect imaging (mainly noise, that is, noise), so it is necessary to balance ISO and image quality.

However, when you say "shoot like a cloudy day" when the light is sufficient, it is not necessarily the ISO setting. The default minimum ISO for D90 is 200 (it can be extended to ISO 100, that is, Lo 1). This situation may be caused by photometry and exposure.

High ISO is mainly used in poor light environment to ensure shutter speed, such as dim indoor light, cloudy day or dusk. When D90 exceeds ISO 1600, noise will obviously affect the image quality. In general, it is best not to exceed 800.