Wednesday, September 9, 2026

RARE EARTH RADIOACTIVE GLASS LENSES MADE BY LEITZ/LEICA


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.


For other articles on this blog please click on Blog Archive in the column to the right

To comment or to read comments please scroll past the ads below.

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Monday, September 7, 2026

COMPARISON OF SENSOR VS FILM RESOLUTION and 135mm, 200mm, 250mm - LEICA, NOVOFLEX, STEINHEIL, MEYER OPTIK LENS COPARISON


By Heinz Richter


In a television advertisement a while ago the statement was made that, if it is on the internet, it must be true. That reminded me of an article comparing film to sensor resolution.  The writer boldly stated that most films have a resolution of at least 300 l/mm (lines per millimeter).  Of course that was overstating things by a huge margin.  I don’t mean to say that there aren't films that can attain such high resolution figures, but all films?

Resolution is generally tested by taking photographs of test targets which show a pattern of white lines in an ever decreasing size against a black background.  Eventually the lines will become so small that the film, the sensor or the lens, can no longer distinguish the white lines from the black spaces in between.  One white line and the adjacent black space are referred to as 2 l/mm (lines per millimeter) or 1 lp/mm (line pair per millimeter).

 
Typical test target

It is a known fact, however, that evaluating resolution with test targets does not render very conclusive information.  The white lines and black spaces in between constitute a very high contrast.  This makes it substantially easier for the film (or a lens) to separate the two.  Reducing contrast by using grey lines on a black background would render substantially different results.

Another major factor influencing resolution is the grain structure of the film.  A film image is made up of silver halide clumps which show up in form of grain.  The smaller the silver halide clumps or the grain, the finer the detail that can be shown.  Faster films simply do display coarser grain which in turn lowers the resolution of a film.

        

 
      These three images are from a fine grain negative (Agfapan APX 25).
The first was scanned from an 8x enlargement, showing the entire negative area.
The second image was scanned from a 16x enlargement.
The third shows a cropped section of the same 16x enlargement
Leica M3, 50mm f/2 Dual Range Summicron
Please note: All three images show the resolution on an enlargement.  The actual film resolution is higher


            
For comparison:  Full image and cropped section from a 5 megapixel digital camera (Leica Digilux 2)

This isn't to say that higher resolution sensors aren't desirable.  The relatively small number of individual sensor elements of a 5 MP camera can only show limited detail.  In order to take full advantage of the capabilities of our lenses, a higher resolution is necessary.

Full frame image Leica SL with Leica Vario-Elmarit-SL 24-90mm f/2.8 ASPH

Cropped section of the above image

Further crop of the original image

Leica M240, 28mm f/2.8 Elmarit

Cropped section of the above image

Finally, the structure of the emulsion or emulsion layers influences film resolution because in any case, light traveling through the emulsion, will scatter and thus reduce resolution as well.

Subsequently, to say that most films have a resolution of 300 l/mm is patently false.  As a matter of fact, only few commercially available films even have that high a resolution.

Researching this topic, I came across a report written by Joseph A. Schantz, Assistant Head of Research and Development Department at the Naval Photographic Center in Washington, DC.  He wrote that since 1963 the Navel Photographic Center and the Naval Air Systems Command, as a matter of continuous policy, have expanded efforts to upgrade 35mm photography on a systematic basis.  The aim of this work was not only to improve the quality of documentary and reportage photography but also to improve intelligence collection capabilities of the Navy’s cameras.

According to the research done by Mr. Schantz, the best resolution obtainable with conventional, slow speed films, like the old Agfapan APX 25, is 250 – 300 l/mm compared to 550 l/mm with the Agfa High Contrast Copy Film and 600 l/mm with Kodak 5069 and 3414 film.

Kodak High Contrast Copy Film when processed in the POTA developer of Marilyn Levy (Levy, M., “Wide Latitude Photography,” Science and Eng. Vol. II Number I, January, February 1967) yield excellent high resolution negatives with adequate film speed.  The Agfa High Contrast Copy film gives a practical combination of good resolution and emulsion speed.

In addition, C. B. Neblette in his book “Photographic Lenses” clearly states: "The resolving power of a lens-film combination is not fixed by the film alone, but by both the lens and the film (or sensor). Resolution is determined principally by the sharpness of the image (lens resolution).  But it is profoundly influenced by the tone producing properties of the receptor (film or sensor) and its ability to reproduce steep gradients.  For that reason, resolution cannot be regarded as an exclusive property of the lens."

For the average films available today, a more modest resolution of 100 to 200 l/mm is a realistic figure, based on film speed and general properties of the film.  Black and white films generally have a higher resolution than color films.  The former Agfapan APX 25, for instance, had a resolution close to 300 l/mm while Fuji Velvia 50 was rated to resolve 160 l/mm.

To make film resolution more understandable in this comparison, let’s refer to the smallest detail a film can show as pixels.  On a standard 24 x 36mm 35mm frame, a film with a resolution of 100 l/mm would render a total of over 8,6 million pixels.  That increases to over 19,4 million pixels with a film resolution of 150 l/mm and over 34,5 million pixels with a 200 l/mm resolution.

Of course, a 35mm negative or transparency is of little use just by itself.  Today transparencies generally are scanned and then further processed digitally.  Does anyone still use a slide projector?  Many film users still make their own enlargements, mostly from black and white negatives, or the negatives are scanned for further processing.  Regardless how films are used, any further processing will have an image degrading effect, based on the slide projector, enlarger or scanner used and by their respective quality.  With other words, the resolution figures for films are a theoretical value that can never be fully realized.

For more details on this topic go to LEICA Barnack Berek Blog article “LEICA LENSES – WHAT GIVES THEM THEIR OUTSTANDING QUALITY.”  However, without going into the details of that article, just one comment about lenses:  Most people consider resolution of a lens to be the most important measure of lens performance.  While that is important, the contrast level of a lens is at least equally important.  This refers to the lens' ability to distinguish between very similarly shaded objects.  A lens with a low contrast level often cannot make that distinction and no increase of contrast during printing or in post production is able to make up for that.  It is actually the fact that a higher contrast level of a lens can result in sharper appearing detail.

Most test targets used to measure resolution use white bars on a black background, 
which constitutes a rather high contrast.  However, if the black bars on a white 
background were replaced with grey bars of various density on a grey background, 
a low contrast level lens would quickly be incapable of distinguishing between the 
bars and the background.

The lens in the top example has twice the resolution of 
the one in the bottom example.  
But the lens in the bottom example has twice the contrast level
 which results in a definitely sharper appearing image

How does this compare to digital sensors?  With few exceptions, top level full frame (24 x 36mm) cameras currently have resolution levels of approximately 25 megapixels.  The general belief is that the higher the pixel count, the better the image quality.  That is correct in as much that the smallest detail a sensor can resolve is the size of the individual pixels.  The new Leica M10-R and M11, which increased the megapixel count to 40+ and 60, have proven to be able to deliver finer detail compared to cameras with a 25 megapixel sensor.  However, there is a lot more to that than meets the eye.  The new CMOS sensors in the new Leica M11, M10, the Leica M (Typ 240) as well as the Leica SL models have definite advantages over conventional CMOS sensors.  For a more detailed description of digital sensors and some of the major differences, got to LEICA Barnack and Berek Blog article “THE PIXEL RACE - DOES IT REALLY MAKE SENSE?”

pixel diagram
Section of a typical sensor
 Image courtesy of  Red Dot Forum

CMOS sensor
Conventional CMOS sensor with deep pixel wells and flat microlenses

MAX CMOS sensor
Leica CMOS sensor with very shallow pixel wells and tall micro lenses, allowing for larger pixel area

Unlike film, digital sensors will render the same contrast level up to the finest detail.  This has the result that the finest detail becomes less visible. A color image is made up out of RGB (red, green, blue) image elements.  With the exception of the hardly ever used Foveon sensors, digital sensors can record only in black and white.  In order to obtain a color image, the light passes through an array of red, green and blue filters, the Bayer filter grid.  This means that the total number of pixels in a sensor are exposed to either red, green or blue light only.  To form a color image, the information obtained from the sensor is then processed by interpolation in the camera or by raw conversion software.  It takes the pixels of each color and assigns all colors to each pixel.  With other words, the software will take a red pixel, for instance, and assign theoretical green and blue values as well to form a complete color image.  As good as these types of software have become, there are certain losses involved.

With lower quality cameras these losses can be as much as 50 percent of the resolution.  The only exception to this is the Leica M Monochrome.  Here the Bayer filter and interpolation software is eliminated to record just black and white images.  See LEICA Barnack and Berek Blog article “MONOCHROME SENSOR - WHAT IS THE DIFFERENCE.”  The result is an unsurpassed image quality and tonal range.

 

In the final analysis, just as there are definite performance differences among films, there are also considerable differences among sensors.  CCD sensors used to be the choice of most camera manufacturers.  These have been widely replaced by CMOS sensors.  In this respect, Leica is no different.  Many people are under the mistaken impression that the CCD sensor in the Leica M8 or M9 delivers superior results than the current CMOS sensor in the Leica M (Typ 240) or M10 and M11 models.  A recent comparison test by David Farkas of the Leica Store Miami thoroughly debunked that.  He took this very subject to task in a three part series in the Red Dot Forum.  See LEICA Barnack Berek Blog article “LEICA M (TYP 240) VS LEICA M9”.

The debate of which is better, film or digital sensors, cannot be answered with any certainty because the large differences among films and sensors.  What can be said is that both film and sensors are capable of delivering very high quality images.  In many cases they do exceed the requirements of the photographer since extreme cropping or enlarging is necessary to even reveal the limits of their capabilities.  Thus, it is more a matter of personal choice than effective differences pointing to one or the other medium as being superior.

As for myself, I used to spend many hours in my professional custom black and white lab developing films and printing with a Leitz Focomat V35 as well as medium and large format enlargers.  Having switched to digital, I don’t miss analog photography at all, and I can say with certainty that I am not compromising the overall quality of my work by having done so.

Complementing the above article, is a comparison of four similar lenses by four different manufacturers.

135mm, 200mm, 250mm - LEICA, NOVOFLEX, STEINHEIL, MEYER OPTIK LENS COPARISON


Leica 135mm f/2.8 Elmarit



By Heinz Richter

When my father gave me my first Leica, a Leica III with 50mm f/2 Summar, it was soon followed by a 135mm f/4.5 Steinheil Culminar.  It served me well and even after all these years I still have the lens sitting on my desk.

Along the way I also came into possession of a Meyer-Optik Görlitz 250mm f/5.5 Tele Megor.  It came with an Exacta mount.  I had no intention to keep the lens, primarily because it was useless on any of my Leica cameras at the time.  To have a better chance of selling it, I converted it to a Nikon mount.  Well, for some reason I still have the lens.  As a matter of fact, with a Nikon to Leica M adapter I can even use it on my Leica M240.

Both lenses date back to the early 50s

I got the idea to take some test shots with these two lenses and compare them to my 135mm f/2.8 Elmarit and 200mm f/3.8 Novoflex.  Both those lenses have proven to be excellent performers and I use them regularly.

To make this comparison test as neutral as possible, I set my camera on a tripod and shot the same subject at the same distance with all four lenses.  To maintain a reasonable exposure time the camera was set to ISO 1000.  Each lens was shot wide open and then stopped down through the various apertures to f/16.  All four lenses were focused with the electronic Visoflex, wide open.  I did not refocus for any of the smaller apertures.

All images are raw, unaltered JPG files.

Looking at the results, it is obvious that the Leica and Novoflex lenses are noticeably better at all apertures.  They should be because they are substantially newer than the other two.  But in a pinch one might argue that the Culminar and the Tele Megor are acceptable, as long as you have the possibility to use them at their best performing aperture.

Maximum Aperture

Steinheil 135mm f/4.5 Culminar @ f/4.5

Leica 135mm f/2.8 Elmarit @ f/2.8

Novoflex 200mm f/3.8 @ f/3.8

Meyer-Optik Görlitz 250mm f/5.5 Tele Megor @ f/5.5

Steinheil 135mm f/4.5 Culminar @ f/4.5

Leica 135mm f/2.8 Elmarit @ f/2.8

Novoflex 200mm f/3.8 @ f/3.8

Meyer-Optik Görlitz 250mm f/5.5 Tele Megor @ f/5.5

Steinheil 135mm f/4.5 Culminar @ f/4.5

Leica 135mm f/2.8 Elmarit @ f/2.8

Novoflex 200mm f/3.8 @ f/3.8

Meyer-Optik Görlitz 250mm f/5.5 Tele Megor @ f/5.5

Best Aperture

Steinheil 135mm f/4.5 Culminar @ f/8

Leica 135mm f/2.8 Elmarit @ f/5.6

Novoflex 200mm f/3.8 @ f/8

Meyer-Optik Görlitz 250mm f/5.5 Tele Megor @ f/11

Cropped Images

In the past I have written about the advantages of high performing, very sharp lenses and the ability to crop their files to give the field of view of a longer lens.  Since the 250mm Meyer lens is the longest focal length in this comparison, I cropped the best files of the other three lenses to give the same field of view.  I added the file of the 250 for comparison.

Steinheil 135mm f/4.5 Culminar @ f/8

Leica 135mm f/2.8 Elmarit @ f/5.6

Novoflex 200mm f/3.8 @ f/8

Meyer-Optik Görlitz 250mm f/5.5 Tele Megor @ f/11
This image is not cropped, for comparison only

Adjusted Images

I rarely use images straight out of the camera because I found that in most instances, these can be improved with Photoshop, Lightroom or similar programs.  For the final comparison I  cropped images of all four files and adjusted them for density and also added some sharpening in Photoshop.  



Steinheil 135mm f/4.5 Culminar @ f/8

Leica 135mm f/2.8 Elmarit @ f/5.6

Novoflex 200mm f/3.8 @ f/8

Meyer-Optik Görlitz 250mm f/5.5 Tele Megor @ f/11

VERY SMALL SECTION CROP


For the final comparison I posted the same, optimized images cropped to a very small section of the original image..


Steinheil 135mm f/4.5 Culminar @ f/8

Leica 135mm f/2.8 Elmarit @ f/5.6


Novoflex 200mm f/3.8 @ f/8

Meyer-Optik Görlitz 250mm f/5.5 Tele Megor @ f/11\

Final Thoughts



Looking at the results, it should come as no surprise that the Leica 135mm f/2.8 Elmarit and the 200mm f/3.8 Novoflex outperformed the other two lenses by a relatively wide margin.  As a matter of fact, the differences are actually less noticeable here because of quality losses due to compression.  It must also be noted that the Leica 135mm Elmarit showed optimum performance already at f/5.6.  I did not show any images at apertures smaller than f/11 because all lenses showed a loss of image quality starting at f/16.


For other articles on this blog please click on Blog Archive in the column to the right

To comment or to read comments please scroll past the ads below.

All ads present items of interest to Leica owners.

_______________________________________________________________________

EDDYCAM - the first and only ergonomic elk-skin camera strap     
 www.eddycam.com        

      



Buy vintage Leica cameras from 
America's premier Leica specialist 
www.tamarkin.com

 http://www.tamarkin.com/leicagallery/upcoming-show


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Please make payment via PayPal to GMP Photography

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