Noise is the addition of unwanted grain or splotches of color in our digital photographs. It can occur by using a high ISO such as 6400 or using very long shutter speeds that last into the minutes. In some cases, noise is a necessary evil that we need to accept, while in others, we should do everything possible to avoid it. As night photographers we need to understand the limits of our cameras and the effects of pushing them too far.
As you may have guessed from experience with your camera’s settings, there are two types of noise: High ISO Noise and Long Exposure Noise. Both are exactly what they sound like.