[Leica] Monster High-tech 50mm 1.4 from Sigma and everyone else

[drodgers at casefarms.com (David Rodgers)]

Marty,

Thanks for your excellent and very informative post. I have a few
questions that perhaps you, or someone else, can answer. First, how
important is distortion for photography outside of architecture?
Secondly, is there much sample variation in modern lenses (my assumption
would be less than in the past, but sometimes I wonderA)? Finally, are
lenses today really any better overall than lenses from say 25 years ago
-- or are they just better in some ways, at the expense of other ways?

I don't shoot any architecture anymore, though at one time I did. I know
that for me to notice distortion now, a lens has to be pretty bad. I can
also live with a little barrel or pincushion, because in a critical
situation I can fix it with software. But the moustache distortion found
in some multi-asph consumer grade zooms (I haven't seen it in primes,
but I haven't bought any new primes in a long time) is impossible to
correct. 

DaveR 

-----Original Message-----
From: Marty Deveney [mailto:freakscene@weirdness.com] 
Sent: Wednesday, February 04, 2009 6:52 PM
To: lug@leica-users.org
Subject: [Leica] Monster High-tech 50mm 1.4 from Sigma and everyone else


>Is that why they call it Double Gauss?

A Gauss lens is a lens with a positive meniscus lens on the object side
and a negative meniscus lens on the image side.  This design was
invented by Carl Freidrich Gauss in 1817.  The negative lens corrects
for chromatic aberration.  A *double* Gauss lens is two Gauss lenses
back to back so you have two positive meniscus lenses on the outside
with two negative meniscus lenses inside them.  Traditional designs of
this type are symmetrical. 

>He talks about the Summicron coming from a Taylor Taylor Hobson design.

The double Gauss design was radically improved by Paul Rudolph's
improvements made while working for Carl Zeiss which consist of
replacing the single negative meniscus lenses with cemented doublets (to
make a six-element symmetrical lens).  Taylor and Hobson's f/2.0 Opic
and Speed Panchro designs originated in the 1920s and are evolutionary
improvements on Rudolph's designs.  Most modern double Gauss designs owe
their origins to these revolutionary designs.  The original
seven-element Summicrons were a further evolution for the type, but were
not symmetrical.  The later six-element 50mm Summicrons are double Gauss
designs derived from Rudolph's design.

Sigma have really shaken things up here in an interesing way.  This EX
DG HSM lens has an aspherical element, like the Leica M 50/1.4 asph, but
I don't think it has afloating element which the Leica does.  Sigma have
moderated some of the aberrations that a floating element corrects for
by making the lens BIG.  It weighs as much as a Noctilux but the front
element is 50% larger.  It's a monster all right.  

The new AF-S Nikkor I tried was disappointing in many ways - it
displayed a lot of distortion, didn't seem to be designed for use wide
open and has observable focus shift.  It's not the lens for my Nikon
SLRs I was hoping for.  I didn't ever anticipate owning a Sigma lens,
but maybe I will.

Marty


Gallery: http://gallery.leica-users.org/v/freakscene


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