By definition the ISO is a measure of the level of the camera sensor to light sensifitas. The higher the ISO setting the more sensitive we terhada sensor light.
To get a clear picture of our camera's ISO setting (ASA in the case of photographic film), just imagine about a bee community.
> An ISO is a worker bees. If I set my camera at ISO 100, meaning I have 100 worker bees.
> And if my camera set at ISO 200 it means I have 200 worker bees.
The task of each worker bees are picking up the light entering through the lens of a camera and make a picture. If we use an identical lens and aperture equally we set at f/3.5 but I set the ISO at 200 while you 100 (think again about the worker bees), then the image got who will finish more quickly?
1. When we add ISO setting of 100 to 200 (in the ever constant aperture – aperture in the key us f/3.5 or through the Aperture Priority mode – A or Av), we shorten the time required in the making of a photograph in the camera sensor we get half (2 times faster), from shutter speed 1/125 to 1/250 of a second.
2. When we add more ISO to 400, we trim the time making up half the photos again: 1/500 sec.
3. Each time the esksposur shorten the time by as much as half, we call the raise esksposur by 1 stop.
You could try this sense in the case of aperture, shutter speed set we try always constant at 1/125 (or Shutter Priority modes – via S or Tv), and ubah-ubahlah your ISO setting in multiples of 2; Missal from 100 to 200 to 400 ... etc, see change your aperture magnitudes.