Every +2 stops is x2 to the f-number. Every +1 stop is roughly x1.4 (more exactly x square-root of 2) to the f-number. After a while, the progression (+1 stop each time) 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 should come naturally to you.
Garion, I was reading and following this thread. Your this information is very enlightening to me. I have never thought of it in such an exact way. Thank you.
I have a question here: do these terms 'increase by 1/3 stop, 1 stop, 2 stops' appply to , say, shutter speed and ISO too?
To put it in a physical context, everytime you go UP a stop, you are letting in twice as much light (with regards to aperture or shutter speed).
That is, you are opening the shutter twice as long (1/30s --> 1/15s) or doubling the size of the aperture (f/2 --> f/2.8)
ahhh, but why 2 --> 2.8? Shouldn't it be 4?
the formula for area of a circle is PI - r squared. [secondary, or was it primary school maths?]
Multiply PI x 2(squared) vs PI x 2.8(squared) and one result is double the other.
So the diameter (or radius, no difference in this context) of the circle increases by a multiple of approximately 1.4, but the area of the circle doubles.