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

f-stop to light transmission % ratio question
 

Hi Tom,

Saying what the other posters have said in other terms, if you open up a
lens from say f/2.8 to f/2, you are increasing the radius of the
aperture circle by a ratio of 1.414, thus doubling the square area of
the aperture circle, thus allowing twice as much light to pass through
in a given amount of time.


Francis A. Miniter


Tom Gardner wrote:

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?