[Leica] inscribed f/stops

[Jim Brick <jim_brick@agilent.com>]

Usually, in the world of engineering, all of the parameters are worked out
before hand. The design is done utilizing all of the parameters, such as
transmittance of the glass and coatings, and the optical formula and lens
diameters all combined, are worked out to give precisely the proper
f/stops. Therefore, an f/2.8 lens is designed to be an f/2.8 lens. And the
diaphragm is set-up to give precise f/stops from f/2.8 to whatever (f/16,
f/22, ...). The engineering is done up front. After that, it's just
manufacturing, assembly, and testing. Perhaps this is why a Leica f/2 lens
is bigger around than a brand-x f/2 lens?

I believe some manufacturers create a lens, then figure out what they have
afterward. If it is within a 1/2 stop of something, they'll call it that
something. Most of these manufacturers have fully automatic cameras that
the lens goes on. The built-in meter figures it out so that it makes no
difference if an f/1.4 lens is really an f/1.79 lens. This is why I won't
own a variable f/stop zoom. You never know at what f/stop the lens is set.
They are made for auto exposure cameras.

I use M on my R cameras. Rarely A or T, Never P. I use D or M on my
Hasselblad. I use S on my Linhof. "S" stands for "Slow."

I have complete confidence that Leica, Zeiss, Schneider, and Rodenstock,
make lenses that represent exactly what they are advertised to be.

Jim


At 01:53 PM 1/8/01 -0800, Paul Chefurka wrote:
>If they do, then I don't believe they can correctly call it an f-stop.  An 
>f-stop is a mathematical ratio.  If they modify it to take transmittance 
>into account, then they're using t-stops.  Of course they could be using 
>t-stops, but calling them f-stops so as not to confuse the great unwashed.
>
>Paul
>
>-----Original Message-----
>From: Pascal [mailto:cyberdog@attglobal.net]
>
>but I thought (actually, have read) in Leitz/Leica litterature that Leica 
>always uses the "true" (photometric) f-stop, unlike most of their 
>competitors... ;-)
>
>Pascal