The reason of thick particles in photographic pictures.

The ISO (sensitivity) setting of digital cameras is too high, and generally lower than 400 will be more appropriate. Of course, it has something to do with the light intensity when shooting. Good light, sensitivity of 200-400, not higher than 400; The light is not good, it is recommended to use flash or light distribution (the simplest is light bulb), and the sensitivity should be kept at 400 as far as possible, and not higher than 800 as far as possible. The average digital camera will have more noise above 800 (that is, what you call coarse particles).