Re: [Leica] F stop: how accurate is a 1.4?

["Timothy R. Kuntz" <covbldrs@usit.net>]

B.D. -
  You are of course joking!  I thought it was commonly understood that, although most think they understand this, in reality it's all magic, well documented by mathimatical Bravo Sierra.
Tim K

- ----- Original Message ----- 
From: "B. D. Colen" <bdcolen@earthlink.net>
To: <leica-users@mejac.palo-alto.ca.us>
Sent: Wednesday, March 08, 2000 4:24 AM
Subject: RE: [Leica] F stop: how accurate is a 1.4?


It would be fun to see those of you who understand this stuff and are firing
calculations back and forth put some sort of professional identification
after your names...i.e., Albert Einstein Scholar at The Institute for Arcane
Mathematical Theora..:-)



- -----Original Message-----
From: owner-leica-users@mejac.palo-alto.ca.us
[mailto:owner-leica-users@mejac.palo-alto.ca.us]On Behalf Of Garrelfs, R
(Rick)
Sent: Wednesday, March 08, 2000 9:54 AM
To: 'leica-users@mejac.palo-alto.ca.us'
Subject: RE: [Leica] F stop: how accurate is a 1.4?



> 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.


Hi Richard,

in fact, I think we agree completely. The only difference is:
You have interpreted the "1.4" designation as "exactely 1 f-stop less than
exactely 1".
In other words: 1.4 is really 1.41421..... etc.

I have interpreted 1.4 as just that: 1.4, meaning it may well be less than
exactely 1 f-stop.
We know the 1.5 only with one digit accuracy too, so when doing the
calculation I only take 1 decimal significance, and then you also come to
0,2 f-stop difference
(instead of 0,199, or 0,169 for that matter).

But I think perhaps the most useful answer would be: the guy who posted the
Dilbert scene was probably right :)


Kind regards,

Rick Garrelfs


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