The concept of what ISO sensitivity is is one of the basic ones. It is necessary even for a novice photographer, of course, a professional cannot do without it.
ISO sensitivity is a measure of the camera’s perception of the light it receives. A high ISO provides the ability to take pictures in dimly lit rooms. Only a few years ago, the ISO sensitivity was not a characteristic of the camera, but of the film itself, and for shooting several frames with different levels of lighting, the photographer needed to change the film, choosing the most suitable one. Today, both professional (SLR and mirrorless) and amateur (digital) cameras have the function of manual and automatic ISO level control, which makes it possible to take frames with different photosensitivity by recording them on the same memory card.
With insufficient lighting for proper exposure, it is not always possible to use an external (and internal) flash. It is in such cases that you have to change the ISO value to a higher one or switch to its automatic setting.
In addition, adjusting the level of photosensitivity can help if it is not possible to increase shutter speed and in the absence of a tripod. In this case, using higher ISO speeds will increase shutter speed.
However, it would be too simple if the constant use of large ISO values ​​did not have a side effect. After all, matrices for cameras are designed in such a way that increasing ISO increases their sensitivity. And in this case, not only a greater amount of light is recorded, but also the so-called noises.
Determines the range of optimal ISO values ​​for the
size of the camera
matrix . The larger it is, the lower
the noise level is even at maximum ISO values. In cameras (both “DSLRs” and “soap boxes”) today basically a matrix of at least 2.3 is installed. "
This should be understood in order to prevent a fairly common misconception that sometimes happens with beginners: you should not think that the more megapixels in the camera, the better. Just the relatively high number of megapixels, which some camera manufacturers are trying to put in the matrix, can significantly reduce the quality of images in terms of excessive noise. Therefore, do not blindly believe in advertising.
Thus, shooting at maximum ISO values ​​is possible only when it is justified:
• If you have a choice between whether to take a picture with noise or not at all.
• If the shooting conditions do not allow the use of the flash.
• If you plan to print small format photographs in which noises will be almost invisible.
• If you can reduce noise by processing.
And when shooting in open space with sufficient natural light, the best choice is ISO sensitivity set to the minimum value. This is how the best shots come out.