A Photography forum. PhotoBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » PhotoBanter.com forum » General Photography » In The Darkroom
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

f-stop to light transmission % ratio question



 
 
Thread Tools Display Modes
  #1  
Old January 24th 04, 03:43 AM
f/256
external usenet poster
 
Posts: n/a
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


  #2  
Old January 25th 04, 04:07 AM
Francis A. Miniter
external usenet poster
 
Posts: n/a
Default 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?





 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump


All times are GMT +1. The time now is 11:16 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2004-2018 PhotoBanter.com.
The comments are property of their posters.