Understanding ISO Concept

By the definition of ISO is a measure of the level of the camera sensor sensitivity to light. The higher the ISO setting, the more sensitive we terhada light sensor.

To get a clear picture of our ISO setting on the camera (in the case of film photography ASA), think about a bee community.
1. An ISO is a worker bee. If my camera set at ISO 100, it means I have 100 worker bees.

2. And if my camera set at ISO 200 means I have 200 worker bees.
Is the duty of every worker bees collect light coming through the lens of a camera and make a picture. If we use the identical lens and aperture together we set at f/3.5 but I set the ISO at 200 while your 100 (think again about the worker bees), the images have who will finish faster?

In outline:

1. When we increase the ISO setting from 100 to 200 (the aperture is always a constant - we lock the aperture at f/3.5 or through Aperture Priority mode - A or Av), we shorten the time needed in making a picture in our camera sensor by half (2 times faster), shutter speed of 1/125 to 1/250 sec.

2. When we add more ISO to 400, we cut back to half again making photographs: 1/500 sec.

3. Whenever esksposur shorten as much as half, we call esksposur increase by   1 stop.

You can try this sense in the case of aperture, shutter speed set we try always constant at 1/125 (or via the Shutter Priority mode - S or Tv), and change-change your ISO setting in multiples of 2, for example from 100 to 200 to 400 etc, look at the amount of change your aperture.