> f/11 is, in fact, 2^(7/2) = f/11.31 that rounds to f/11
> f/22 is, in fact, 2^(9/2) = f/22.63 that rounds to f/23
>
> But 23 is not the double of 11, so I suspect that 22 is used in order to
> obtain the series: f/1.4, f/2.8, f/5.6, f/11, f/22 (odd) and f/2, f/4, f/8,
> f/16 (even)
>
> As can be seen you always double the f/ number for a two stop closing.
Using the "doubling rule", I would think that the sequence
f/5.6, f/11, f/22, f/45 seems more plausible and accurate
than the sequence f/5.6, f/11, f/23, f/45.
> OTOH, f/45 is the correct value but it's not the double of f/22. But I
> suspect that f/45 is not an usual f/number.
En contraire! (forgive my poor french)
E.g.: Just add a 2x to your 70-200 2.8L, and - voila - your
smallest aperture is now f/45 (two stops down from f/22).
Also, in the world of Large Format (sorry, slightly off-
topic ...) smaller apertures like f/32 or f/45 are quite
common. Ever heard of the f/64 Group?
Lars
--
Lars Michael [EMAIL PROTECTED]
87GT http://www.citilink.com/~larry/gallery
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