Archived posting to the Leica Users Group, 2000/03/06
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The computation is based on the ratio between the lens opening and the
focal length. I compute the difference between f1.4 and f1.5 to be 22.4% of
an f-stop.
The difference between f1.5 and f1.4 seems to be 22.4% of an f-stop
calculated as follows:
The diameter of a 50mm lens of f2.0 is 25.0mm. (50 devided by 2.0 =
25.0mm)
The diameter of a 50mm lens of f1.5 is 33.3mm (50 devided by 1.5 =
33.3mm)
The diameter of a 50mm lens of f1.4 is 35.7mm (50 devided by 1.4=
35.7mm)
The difference between f2.0 and f1.4 is 10.7 mm which is 100.0% of the
stop.
The difference between f2.0 and f1.5 is 8.3 mm which is 77.6% of the
stop.
The difference between f1.4 and f1.5 is 2.4 mm which is 22.4% of the
stop.
Roland Smith
roland@dnai.com
- ----- Original Message -----
From: John Collier <jbcollier@home.com>
To: <leica-users@mejac.palo-alto.ca.us>
Sent: Monday, March 06, 2000 9:17 AM
Subject: Re: [Leica] 50mm f1.5 Nokton question
> This from a long time ago, with my memory that is about a week, but I
> thought it went:
>
> 1.0~whole stop
> 1.1~ -1/3
> 1.2~ -1/2
> 1.3~ -2/3
> 1.4~ whole stop
> 1.5~ -1/3
> 1.7~ -1/2
> 1.8~ -2/3
> 2.0~ whole stop
> etc
>
> Please correct me if I am wrong and I will order the Nokton today.
>
> John Collier
>
> > From: Marc James Small <msmall@roanoke.infi.net>
> >
> > At 06:45 AM 3/6/2000 -0700, John Collier wrote:
> >> Why did they make it a 1.5 and not a 1.4? Sentimental reasons! I know
it is
> >> only a 1/3 stop but it is annoying.
> >
> > John
> >
> > I believe it is more like 1/7 of a stop.
> >
> > Marc
> >
> > msmall@roanoke.infi.net FAX: +540/343-7315
> > Cha robh bas fir gun ghras fir!
> >
>
>