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Old January 24th 04, 04:43 AM
f/256
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Default f-stop to light transmission % ratio question


"Tom Gardner" wrote in message
gy.com...
Is there an easy formula to translate f-stops to the percentage of light
transmission? As each stop is 50% of the previous stop, where did the
numbers come from?


Transmission of light is not associated to f/stops, that is a function of
the lens characteristics, but, I think you mean how much light "X" aperture
ALLOWS compared to a "Y" aperture. If so, the formula is

( X^2 / Y^2) * 100

for instance, comparing f/32 with f/4

(32^2 / 4^2) * 100 = ( 1024 / 16 ) * 100 = 6400%
f/4 allows 6400% more light than f/32

The other way around:

(4^2 / 32^2) * 100 = 1.5625%
f/32 allows just 1.5625% of the light f/4 allows

Where it comes from?: it seems to have come from hell, for those that forgot
their 6th or 7th grade math! :-)

Guillermo