OK, here goes:
Camera lens F Stops use an apparently odd set of numbers. The problem is that the amount of light entering the lens is governed by the area of the aperture; a squared function, not a linear one. If the F Stops increased in a 2 fold linear form (1,2,4,8...) then the exposure would not increase two fold but as a square of this, which is 4 fold. Opening the aperture by one F Stop would therefore quadruple the exposure as 2² = 4. So a set of numbers is needed, that when squared comes to 2, to give the double exposure required. In other words, numbers need to increase by √2, as √2² = 2, to give twice the area.
• 1 x √2 = 1.4
• 1.4 x √2 = 2
• 2 x √2 = 2.8
• 2.8 x √2 = 4
• 4 x √2 = 5.6
• 5.6 x √2 = 8 etc.
Hence the familiar sequence of 1, 1.4, 2, 2.8, etc, used on camera lenses. This now means that one F Stop increase doubles the light exposure, and likewise one F Stop decrease halves it.
Example:
As will be shown below, if we start by f/1.0 as the smallest possible f/stop, the next full stop is 1.0xSqrt(2) = 1.414. This is the first f/stop that corresponds to the bottom row. Now
1.414x2 = 2.828
2.828x2 = 5.686
5.686x2 = 11.312
11.312x2 = 22.624
22.624x2 = 45.248
At any rate, I believe this is correct.
Clear as mud!
