Leica KE-7A with 50mm f/2 Elcan
Leica lenses are known for
their quality, state-of-the-art technology and design. To achieve desired
results, Leica optical designers have gone radioactive in the past!
In this piece, published by the International Leica Society, Jason
Schneider breaks down the quirky history behind rare earth glass Leica lenses.
These lenses incorporated elements made of thorium and lanthanum glass because
of their unique optical properties. Both materials emit radiation that can be
measured with a Geiger counter.
Take a step back into
Leica's history and learn more about the design and background of these
legendary lenses.
RARE EARTH GLASS LEICA
LENSES: A QUICK AND QUIRKY
OVERVIEW
By Jason Schneider
Yes, they were (and still
are!) literally radioactive, but they incorporated elements made of thorium and
lanthanum glass because of their unique optical properties
By the late 1940s, the
management at Leica knew they needed to come up with a superlative successor to
the well-respected 50mm f/2 Summitar that had been designed by the legendary
Max Berek in 1937 and had been in production since 1939. By that time, they
were diligently working on a stunning new Leica camera that was to become the
landmark Leica M3 of 1954, and their goal was to grace it with the finest, most
advanced 50mm f/2 lens the world had ever seen.
The assignment fell to
Gustav Kleinberg and Otto Zimmermann, two of the most brilliant optical
designers at E. Leitz Wetzlar and close associates of Berek, who passed away in
October 1949. To create what became the Summicron, a 7-element, a 4-group
masterpiece with elements having shallower curves than those in the Summitar,
they needed to use glass that provided a very high refractive index
(light-bending power), along with very low dispersion (the differences in
light-bending angles for various wavelengths of light.) The classic measure of
the optical dispersion of a glass is its Abbe number; the higher the number,
the narrower the dispersion spectrum, and the easier it is to control chromatic
aberrations, etc.
At the time, the only way
to achieve glass that provided a very high refractive index and a high Abbe
number was to incorporate a “rare earth,” thorium oxide or lanthanum oxide,
into the glass itself. Both materials emit radiation that can be measured with
a Geiger counter, but thorium is significantly more radioactive than lanthanum
because a much larger percentage of it consists of an unstable isotope. The eventual
plan was to use a special Krown Lanthanum glass (later licensed to Schott Glass
Works as LaK9) that was formulated by Broemer and Meinart in Wetzlar’s renowned
glass division. But LaK9 glass wasn’t available until late 1952, and even then
only in limited quantities.
The interim solution: the
very first batch of “stealth” 50mm f/2
Leitz Summicrons, identifiable by having a star (asterisk) engraved after the
word Summitar on their identification rings, and early examples of the correctly
labeled collapsible Summicron dating from late 1951 to 1952, used thorium glass
supplied by Chance Brothers & Co,
Ltd. of West Smethwick, England! For the record, thorium (aka Torio) glass was
used for elements 1, 3, 6, and 7. These lenses are the unique and collectible
“radioactive Summicrons” of lore and legend that tend to acquire a
yellowish-brownish cast over time that can be eliminated by extended exposure
to UV (that is, sunlight.) According to those who’ve shot with a wider variety
of 50mm f/2 Summicrons than I, the earliest Summicrons and the very rare Star
Summitar are quite good but not stupendous in terms of image quality. Later
iterations of the classic 7-element 50mm Summicron (serial numbers
993,000-1.030,000) that employ lanthanum (LaK9) glass provide noticeably better
imaging performance, especially wide open. However, this and subsequent
improvements were the results of tweaks in the optical design, not the type of
glass used. The great Walter Mandler, then chief optical designer at Leitz, was
responsible for many of these optical upgrades, including the design of the
6-element, 5-group, and 6-element 4-group 50mm f/2 Summicrons, both of which
incorporated other types of lanthanum glass.
The 50mm f/2.8 Elmar:
Lanthanum glass gains 2/3 of a stop
While analyzing the
possibility of developing a new, faster 50mm Elmar lens back in the ‘50s, the
Wizards of Wetzlar determined using then state-of-the-art computer-aided design
(CAD) that the latest Red Dial version of the classic 4-element, 3-group 50mm f/3.5
Elmar would be difficult to improve upon at a maximum aperture of f/3.5.
However, if they wanted to increase its maximum aperture by 2/3 of a stop to
f/2.8 and maintain its legendary image quality, they needed to use lanthanum
glass. Indeed, LaK9 glass is employed in the first and last elements of the
original 50mm f/2.8 Elmar of 1957-1974, which was made in screw and M mounts.
Optical performance was further improved in the 50mm f/2.8 Leica-M of
1994-2007, but to the dismay or bokeh aficionados, this version had a 6-bladed
instead of a 15-bladed diaphragm. The 50mm f/2.8 Elmar enjoyed a brief spate of
popularity as the standard lens supplied on Leica IIIg outfits (1957-1960) but
it was produced in fairly limited quantities despite its 50-year production run
(there was a total of 17,461 assigned serial numbers from 1994 to 2005.) It’s a not stellar performer wide open,
especially at the edges of the field, but it’s extremely sharp overall at
moderate apertures and has lovely natural rendition and beautiful bokeh.
Oh, Canada! The exquisite
limited-production Elcan lenses
The fabled Leica KE-7A was
made in Leica’s Midland, Ontario, Canada factory in 1972 and 1973. Its
basically a black finished military version of the Leica M4 that’s been
specially sealed against dust and dirt, has a winterized shutter, and the
bottom plate seamed with extreme glue that enhances its tightness, the legend
“CAMERA STILL PICTURE KE-7A” engraved on its top. Originally made for the U.S.
military, a small number (55 body-lens outfits) were sold to the public found
and their way to civilian collectors. Others had the military I.D. number on
the back scratched off when the camera was decommissioned. A total of only 550
bodies were ever made so any Leica KE-7A is a rare bird indeed.
The standard KE-7A outfit
included the rare 50mm f/2 Elcan (which stands for E. Leitz, Canada) lens, a
unique formula consisting of 4 non-cemented, air-spaced elements designed to
withstand the rigors of extreme weather and service in active combat zones. The
lens, which was designed by Gary Edwards, Walter Mandler, and Erich Wagner, had
a 10-bladed diaphragm providing apertures of f/2-f/16, and it focused down to
30 inches. It was constructed of anodized aluminum, and incorporated lanthanum
infrared-absorbing glass and high refractive index optical glass, so, like the
lenses above it emits radiation. Regrettably, I have never shot with one of
these gems, but it’s reputed to be a superb lens capable of outstanding image
quality even at maximum aperture—which demonstrates what you can achieve with
custom designed, bench assembled optics and mil-spec quality control.
There was a slew of
additional super-rare, limited-production Elcan lenses made in M- and R-mounts
and designed for the military during the Cold War era. All were designed by or
with the input of Walter Mandler, all evidently incorporated lanthanum glass,
and all delivered astonishing performance according to those who’ve used them.
The 66mm f/2 Leica Elcan was an ultra-high-resolution M-mount lens for the
KE-7A reportedly ordered by U.S. Navy and also used by NATO. I haven’t been
able to come up with a diagram, but it evidently had 9 elements, a minimum
focusing distance of one meter, and took E39 filters. In addition to the 50mm
and 66mm f/2 Leica Elcans, Leitz Canada also created a 90mm f/1.0 Elcan, which
must have been a pretty hefty handful, and three ultra-high-resolution R-mount
lenses for Leica SLRs. This latter trio
consists of the75mm f/2 Elcan-R, 180mm f/3.4 Elcan-R, and the 450mm f/5.6
Elcan-R. These lenses were probably not equaled, much less surpassed until the
recent Leica lens designs spearheaded by Peter Karbe.
Perhaps the best way to
conclude this fun exploration is to quote from the cogent comments Phil Forrest
posted on the Rangefinder Forum on 8/8/17 Here’s a lightly edited, somewhat
condensed version:
“The optical properties of
old classic lenses won’t likely be replicated in the near future or ever, for
that matter. Lead, Lanthanum and Thorium glass production were halted as of
2001. For example, the 38mm (Zeiss) Biogon in the (Hasselblad) SWC underwent a
slight formulation change due to the new glass restrictions. Most of the heavy
metal glasses were phased out in the late 70s and 80s due to environmental and
workplace hazards. So, there’s one reason.
But as far as Leica goes,
they have staked their claim into the digital realm. They can’t reissue older
designs due to the restrictions of the digital sensors and the very short lens
registration, 27.8mm…. Leica (is) designing the nodal point of their new fleet
of lenses farther forward so the light rays are more perpendicular to the
sensor…. you can’t use (many superb
classic lenses) on what Leica sees as their future, without workarounds and
image compromise. A 66mm f/2 Elcan could certainly be done but it was a
special, rare, niche lens, which never was intended for use by the general
population. Design, ray-tracing, tooling, sourcing glass, all would be very
expensive, and the sales wouldn’t pay for the investment.”
For the complete article by Jason Schneider go here:
For more information about LHSA, the International Leica Society go here:
Our sincere thanks to Jason Schneider and the International Leica society for allowing us to reprint this article.
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