-----Original Message-----
From: PCACala@xxxxxxx <PCACala@xxxxxxx>
>Hi Windsor:
>
>> I am never quite sure, since FStops are not
>> linear or arithmetic, how much more light I am letting in wide open than
>> the nearest true FStop.
>
>Remember these 1/3 stop increments:
>16, 18, 20 and
>22, 25, 28
>and you can calculate the others by simple doubling or halving of the
numbers.
>To save the trouble, here they are:
>1, 1.1, 1.2
>1.4, 1.6, 1.8
>2, 2.2, 2.5
>2.8, 3.2, 3.5
>4, 4.5, 5
>5.6, 6.3, 7
>8, 9, 10
>11, 12.5, 14
>16, 18, 20
>22, 25, 28
>32, 36, 40
>45, 48
>
>There is some rounding involved, esp. f/8 which is really f/7.7
>
This is an arbitrary relative scale, and what is rounded depends on the
starting number. I would assume f/1 is the original base number. If you
start a higher numerical value and work backwards, different numbers will be
rounded. In fact, most numbers are rounded including f/1.4 if you start at
1. It is based on the fact that the amount of light passed by a lens is
inversely proportional to the square of the f-number.
Doug
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