You have probably noticed that photos sometimes have ripples, grain, or, as it is also called, digital noise. Noise is especially pronounced in photographs taken in low light. For the presence / absence of ripples in photographs, such a parameter as ISO sensitivity is responsible. This is the degree of susceptibility of the matrix to light. It is denoted by dimensionless units – 100, 200, 400, 800, 1600, 3200, etc.
When shooting at the minimum sensitivity (for example, ISO 100), the picture quality is the best, but you have to shoot with a slower shutter speed. With good lighting, for example, during the day on the street, this is not a problem. But if we go into a room in which there is much less light, then it will no longer be possible to shoot at the minimum sensitivity – the shutter speed will be, for example, 1/5 second and at the same time the risk of “stirring” is very high, as the blurry photo due to jitter is called hands
To avoid shaking in low light, either raise the ISO to bring the shutter speed down to acceptable values, or continue shooting at the lowest ISO and use a tripod. When shooting with a tripod at slow shutter speeds, moving objects are very blurred. This is especially noticeable when shooting at night.
ISO sensitivity has a direct effect on the exposure level. The higher the ISO number, the brighter the picture will be at a fixed shutter speed and aperture.