Archived posting to the Leica Users Group, 2000/03/08
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Rick Garrelfs wrote:
> What is the difference between a 1.4 summilux and a 1.5 Noktor?
> Y = 1.5
> X = 1.4
> Ln(1.5) - Ln(1.4) = 0.06899; Ln (sqrt 2) = 0,34657
> difference is: 0.06899/0,34657= 0,19906, or about 0,2 f-stop.
Sorry Rick I do not agree...
I see a small mistake.
Just have a look at my previous calculations.
In fact it does not matter wether you use log or ln but
by calculating the difference between f 1.5 and f 1.4 you have to use the
real values.
So 1.4 is not 1.4 but sqrt 2
{ln(1.5) - ln(sqrt 2)} / ln (sqrt 2) = 0,16993
and this equals +/- 1/6 stop.
You kept me wondering why both our calculation methods gave a different
answer, because mathematicaly they are both the same.
So the Nokton is even a little bit more closer to the 1.4(1.41421...)!!
Richard.