[Leica] 1.8 vs. 1.4!?!?

[kanner at acm.org (Herbert Kanner)]

Hey guys:


1. Ted is absolutely correct: stop worrying about technical 
hair-splitting; it won't make a damn bit of difference to the quality 
of your shots.

2. Here is the exact physics of it. the stop value is the ratio of 
the focal length to the diameter of the effective lens aperture. A 
change of "one stop" is by convention a doubling or halving of the 
exposure. Now the exposure has to be proportional to the area of the 
aperture, thus proportion to the reciprocal of the square of the stop 
value.

Now it gets nasty. Since the exposure now is proportional to "2" to 
the power of the number of stops, i.e. 1 stop multiplies exposure by 
2, 2 stops by 2 squared or 4, 3 stops by 2 to the power 3 or 8, then 
the number of stops of 1.4 vs. 1.8 would be the logarithm (base 2) of 
the square of1.8/1.4 or log (base2) of 1.654, which is 0.725, or 
approximately 3/4 stop.

Peace,

Herb





>I looked up f 1.8 vs. 1.4 thinking it was between a half and a quarter of a
>stop and they are saying its 2/3rds!?!?! Anybody know that that's true?
>
>Where is there a photo calculator that tells you these things?!?!?
>
>--
>Mark R.
>http://gallery.leica-users.org/v/lugalrabs/
>
>
>
>_______________________________________________
>Leica Users Group.
>See http://leica-users.org/mailman/listinfo/lug for more information

-- 
Herbert Kanner
kanner at acm.org
650-326-8204

Question authority and the authorities will question you.