Before you start shooting pictures with your camera it’s important that you select the correct ISO setting either from a button on the camera body or via the menu. The ISO (International Standards Organization) index is a system for calibrating the sensitivity to light of film emulsions and digital sensors; the higher the ISO number, the greater the sensitivity. For almost all cameras the ISO settings go from 100 to approximately 3,200, though the latest digital sensors allow settings of up to ISO 25,000. The lower the ISO number the finer the quality of the image, whether film or digital. As the ISO number increases so does the amount of noise in a digital image and grain in a film negative, breaking up the image and reducing sharpness and detail. Noise reduction can be turned on when shooting at higher ISOs, but it tends to soften the image somewhat. It does not have a benefit at low ISOs. Grain and noise are not necessarily a bad thing, they can be another creative tool used to enhance subjects like foggy mornings and night time shots. and are most effective in black and white shots.
A handy tip is to try and get into the habit of checking the ISO setting each time before you start shooting your shots or you might end up with a lot of pictures on a setting that does not suit the subject. It’s also important to remember you can change your ISO at any time during a shoot. For instance if the light drops suddenly and you find the shutter speed has become too slow for a hand-held camera, you can turn up the ISO and retain your higher shutter speed.