Shutter speed, aperture, and ISO are the three components of photography. ISO is that important part of the camera that measures the image sensor's gentleness to light. To say it in other words ISO has a remarkable impact on the production of a quality image in photography. Similar to the other two settings ISO is responsible to control the brightness of photos. When you use it with perfection, it will offer you the best results.
In simple words, ISO is one of the settings of camera that brighten or darken the photos. To have bright photo ISO can be increased. Hence, it is a good component for taking photos/images in a dark environment.
However, increasing the ISO has its own implications. A photo taken by increased ISO, shoes a lot of grain, noise, as it may also be said and it may be of no worth for its utility. So brightening the photos via ISO is not a good deal. It is best for photography in ark environment.
As it is evident from above, by doubling the ISO speed you are doubling the brightness of the photo. For example, a photo at ISO 400 will be twice brighter than ISO 200, which will be twice brighter than ISO 100.
The lowest ISO in your camera is your 'base ISO'. This setting is of utmost importance, as it gives the best performance or produce the highest image quality and minimizing the possibility of grain or noise as much as possible. In most of the digital cameras, the base ISO is 100. It is suggested that you should always try to stick to the base ISO to get the highest image quality. However, it is not possible always, when working in low-high conditions.
Though, it is always recommended that it is ideal to use low ISO's, in many cases the necessity to use high ISO becomes a necessity in order to take a good photo, in the first place. The reason behind it that you are often fighting against motion blur and you will need to pick between a sharp photo at a high ISO or a blurry photo at a low ISO.
In simple words, you should increase the ISO when the light is in scarcity for the camera to capture a sharp, bright photo to any other way.
Aperture setting that provides desire depth of field should be selected.
Set the ISO to base value, and put your shutter speed to whatever setting, as it provides a proper exposure.
If the subject is blurry progressively, raise your ISO and use a faster shutter speed until motion blur disappears.
If your ISO is getting too high and you still have the ability to use a wide aperture, open it up, till the ISO attains a more manageable level even at the cost of your desired depth of field.
ISO is a setting in the cameras, which shows braveness in photography, where the light intensity is low and produces high results without noise or grains, even when the ISO is high. It has made photography more refined.