Lesson Two: Playing with stops

If amount of light collected (similar to water in balloon model) in a setting is x.
If we collect twice of that, 2x then we say we have moved a stop.

We can move stops in exposure by moving up on aperture stops or shutter speed. Shutter speed stops are very simple, from current setting of, say, 1 second you have to go to 2 second. That is double the time. For aperture stops it is not the radius but the area which should double. Since area is proportional to radius square i.e. radius*radius, radius should move by square-root(2) i.e. 1.414. And then couple this with unintuitive F number (which is inverse of radius). For aperture to go up by a spot, the F-number should go down by 1.414.

Best way to try this to use Aperture Priority or Shutter Priority modes, where camera allows one of the aperture or shutter speed to vary and other is fixed to get normal exposure. Change one and see other changing by equivalent amount in other direction.