We use a digital or film camera. We need to be able to calculate exposure properly. But first, we need to understand how the aperture and the shutter work together. We also need to know how film handles light, and the relationship between film light sensitivity and f/stops.
In traditional (film) photography ISO (or ASA) was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking.
One way to improve sharpness in dim light is to increase the camera's sensitivity. This works in places such as theaters and gyms where subjects are too far away for flash to work and where you need a faster shutter speed to eliminate blur. It also is a good way to get pictures without using flash in places such as concerts and museums where flash is prohibited.