Was the Leica screw mount really created by Leitz, Wetzlar?
That’s what everyone says, but one Italian expert begs to differ!
By Jason Schneider
Like most Leicaphiles I’d always assumed, based on the words of experts and historians, that Leitz had originated the 39mm Leica screw mount, aka M39 or LTM, back in 1930, first installed it on the early Leica I (Model C) in non-standardized form, and then standardized it on later Model Cs by adopting a uniform flange focal distance of 28.8mm. The Leica screw mount allowed lens full lens interchangeability among screw-mount Leicas from the standardized Leica I, Model C all the way up to the Leica IIIg of 1957-1960, the last of the screw mount Leicas.
But then I ran across Leica the First 60 Years by Gianni Rogliatti, in which the author states, on page 42: “As early as 1928 the Leica I had an ‘interchangeable’ lens. This was a conversion by Meyer who fitted one of their own f/1.5 lenses by means of a screw mount. As far as can be determined they originated the Leica screw mount. These cameras were advertised from 1928.” Indeed, a picture of a Leica I (Model C) with a 50mm f/1.5 Meyer Kino-Plasmat nicely mounted on it does appear on page 43 of the book, along with an ad by Meyer’s British Distributor A.O. Roth quoting a princely price of 39 Pounds Sterling for the (unnamed) Leica camera, f/1.5 lens, and 3 spools of film (presumably pre-loaded Leica cassettes).
Cover of G. Rogliatti's excellent volume on the first 60 years of Leica.
Leitz’s fastest 50mm Leica lens in 1928 was the not so fast 50mm f/3.5 Elmar! The Meyer 50mm f/1.5 was not just among the first interchangeable lenses for the new Leica (even if not rangefinder coupled since the Leica of that time had no built in rangefinder), it was amazingly fast for 1928. Indeed, the F1.5 Meyer Kino-Plasmat essentially invented Leica superspeed buy it off the shelf low light photography!
Copy of page 42 of Rogliatti's book. Note caption to image and last paragraph of text suggesting that Meyer devised the Leica screw mount.
The Meyer Kino-Plasmat lens, as its name suggests, was originally designed for cinematography, which in most cases meant the 24 x 18mm 35mm cine format, and that raises the questions of if and how well any of these lenses would cover the Leica’s 24 x 36mm format. However, it was by far the fastest super-speed lens of its day and even the films of the day were very slow (ISO 100 equivalent when pushed), so the motivation to mount one on a Leica would have been quite high in any case. Both the nickel-plated Meyer Kino-Plasmat pictured on page 43 and the larger 4-inch (?) one shown next to the lens-less Leica I (Model A) on page 42, bear the name of P. Rudolph. Paul Rudolph (1858-1935), one of the greatest lens designers at Carl Zeiss, was responsible for such legendary lenses as the Zeiss Anastigmat of 1889 (later sold as the Protar), the Planar, and the Tessar (1902). He was hired by Meyer in 1920, where he turned out the highly color corrected Plasmat, and the Kino-Plasmats, the fastest lenses of the mid ‘20s.
Detail image on p/ 42 of Rogliatti's book showing coarse 34mm diameter thread on Leica I (Model A) camera and on 50mm f/3.5 Elmar at right.
The Leica mount legend vs. revisionist history
If the time-honored creation story of the venerable Leica screw mount really turns out to be a myth, it would certainly be ironic, iconoclastic, and wryly amusing to those who scoff at the Leica mystique and cause consternation among Leica fanatics. However, before we can assess the veracity of the claims made my Rogliatti and others that the Hugo Meyer lens company may have invented the Leica screw thread mount that was then presumably “appropriated” by Leitz without any acknowledgement, let’s review the official narrative that has come down to us:
The humble screw mount that Leitz first installed on the non-standardized Leica I (Model C) in 1930 was a simple idea that ultimately transformed the Leica into what many consider to be the world’s first 35mm photographic system. The M39 mount, often called LTM (an acronym for Leica Threaded Mount), or simply Leica Screw Mount, is 39mm in diameter, and has a Whitworth thread of 26 turns per inch (tpi), which works out to a pitch of 0.977 mm, just shy of 1mm. Why Whitworth, rather than, say, metric? Because E. Leitz Wetzlar was a major microscope manufacturer, and the Whitworth system was the industry standard established by the Royal Microscopical Society (RMS) of England. Leitz was already using it for its microscope objectives, so the factory tooling was already set up to produce the Whitworth thread form. True LTM lenses also have a flange focal distance of 28.8mm, but that wasn’t standardized on early Leica I, (Model C) cameras produced prior to December 1930, known as “non-standardized Cs.”
1928 ad by A.O. Roth of London, the UK Meyer lens distributor, showing a fast Meyer lens on what looks liker an early Leica I (Model C).
The first screw mount Leica
The collapsible lenses permanently affixed to the original Leica I (Model A) and the Compur shutter Leica I (Model B) were problematic for Leica photographers who wanted greater optical flexibility. In characteristic fashion Leitz addressed it in the simplest, most direct way possible—they simply installed the M39 mount on what was essentially a Leica I (Model A), creating the Leica I (Model C), Leica Code name LENEU. This allowed you to mount a 3.5cm f/3.5 Elmar, a 5 cm f/3.5cm Elmar, or a 9cm f/4 Elmar on the camera body—but there was an important catch. Since these cameras were literally handmade, with slight variations in lens mount-to-film-plane distance and in the physical placement of the mount itself, each interchangeable lens had to be calibrated to a specific camera body. To ensure a proper match, the earliest iterations of these interchangeable Leitz lenses had the last three digits of the Leica camera body serial number engraved on the lens barrel. A total of 2,307 of these non-standardized Leica I (Model C) cameras were produced in 1930 and 1931, all now virtual museum pieces.
Early Leitz New York ad for the Leica I (Model C) extolling the virtues of its trio of interchangeable 35mm, 50mm, and 90mm lenses.
The issue of full lens interchangeability was resolved in the latter part of 1930 with the introduction of the standardized mount. The distance from the front of the lens mount to the film plane was fixed at 28.8mm, and it remained the same for all screw mount Leicas up until the very last Leica IIIg that rolled off the production line 30 years later in 1960. The standardized mount meant that any Leitz screw mount lenses could be used on any screw mount Leica without individual calibration, a simple spec that, combined with the ingenious rangefinder coupling system that debuted in the Leica II (Model D) of 1932, enabled the little Leica to become the dominant 35mm rangefinder system of the 20[SUP]th[/SUP] century. The first “standardized” Leica I (Model C) bore Serial No. 60501 and all subsequent Model Cs were standardized. Early standardized Leicas have an identifying “O” engraved on the top of the lens mount, and a total of 7,231 standardized Leica I Model C cameras were made.
In 1933 Leitz brought out the Leica Model E, widely known as the Leica Standard, all with standardized lens flanges. The only operational difference between a standardized Model C and the later Model E is that the latter has a smaller diameter rewind knob that extends to make rewinding easier.The M39 lens mount endured in its original form over an evolving succession of literally dozens of I- II-, and III-series Leicas from the ‘30s through the ‘50s, even in the face of a succession of ingenious bayonet mounts introduced by competitors including Contax, Exakta, and Nikon. The LTM mount was slower of course, but it was durable, straightforward, and it worked.
To get back to Mr. Rogliatti, his book, and his contentions regarding the origins of the M39 screw mount, it’s important to examine both his wording and the images in his book with great care before coming to conclusions. Gianni Rogliatti, who passed away in 2012 was an acclaimed automotive journalist, a close friend of Enzo Ferrari, had a warm relationship with the Leitz family, and wrote 3 highly respected books on Leicas including the volume cited. Here are his own words regarding the f/1.5 Meyer lenses fitted to Leica cameras prior to 1930:
“As early as 1928 the LeicaI had an “interchangeable” lens. This was a conversion by Meyer who fitted one of their own f/1.5 lenses by means of a screw mount. As far as can be determined they originated the LEICA screw mount.” Now for starters, the expression “as far as can be determined” is classic journalistic CYA that has essentially the same meaning as “to the best of my knowledge” or “as far as anyone knows.” Rogliatti is a conscientious journalist who’s giving his opinion but hedging his bets. His statement is fascinating but hardly dispositive.
Now let’s turn to the pictures in his book. The photo on page 42 shows a Leica I (Model A) identifiable by its “hockey stick” infinity catch, with its lens removed. To the right side of it is a collapsible 50mm f/3.5 Elmar and to the left of the camera is an unspecified Meyer Kino-Plasmat lens. If you look closely, you can see that both the mount on the camera body (which retains its footage scale) and the screw mount at the bottom of the Elmar,both have coarse threads that don’t look like LTM threads, which are much finer. Also, if you measure the diameter of the mount on the camera and correlate it with the known dimensions of the Leica A body, it works out to about 34mm, much narrower than the 39mm diameter of LTM mount. The unspecified Meyer lens can presumably also screw into the Leica A pictured, but its male screw mount is hard to see.
What’s going on here? If you remove the set screw on the mount of the Leica A you can unscrew and remove the entire “non-interchangeable” 50mm f/3.5 Elmar, revealing a coarse thread measuring about 34mm in diameter. This is the fixed part of the lens’s focusing helical, the moving part being the original threads on the end of the lens that screw in and out as you focus. But if you install a secondary single focusing helical (the kind in which the entre lens turns) on the lens itself you can use the original fixed part of the focusing helical attached to the camera as a de facto threaded lens mount! That’s exactly what’s been done here, and since the Meyer lens pictured also has its own built-in focusing helical all you’d have to do to mount it on the camera is add a coarsely threaded 34mm male screw thread at the rear and screw it directly into the Leica A. This would have been a much easier solution for Mayer, or anyone selling Meyer lenses, than engineering a new mount and modifying the camera. And once Leica came out with the standardized Model C in 1930, Meyer could simply make lenses in 39mm Leica screw mount, which they did in profusion throughout the ‘30s. Significantly, both the Leica display picture and the A.O Roth adof 1928 on page 43 show Meyer lenses fitted to Leica C cameras which would have had standardized or non-standardized 39mm LTM mounts.
As a clincher, even if Meyer had decided to make its own mount and install it on the Leica A it’s highly unlikely that they would have chosen a 26 tpi (threads-per-inch) Whitworth thread that only a microscope maker could love—they probably would have gone metric and made it 39 x 1mm rather than 39 x 0.977. And if Leitz had simply appropriated Meyer’s mount as their own without so much as a by your leave, they probably would have raised a stink.
Despite the weight of all this logical analysis I concede that it’s theoretically possible that Meyer could have pulled this off. After all even Marc Small, author of the authoritative Non-Leitz LEICA Thread-Mount Lenses has stated, “The noted British camera concern of A.O. Roth offered non-standardized Leica A and C bodies as early as 1927 fitted to take interchangeable Meyer 50mm f/1.5 Kino-Plasmat lenses.”
Whether this means that the Leica A bodies were modified with Meyer-designed LTM mounts depends on what you mean by “fitted,” but in my arrogant opinion the Meyer lenses in question were modified to fit the Leica A’s de facto threaded mount, not the other way around, and that by the time the Leica C rolled around it already had a Leica screw mount, complete with those Whitworth threads.
Or maybe not. According to the experts at LeicaShop Vienna the LTM mount was invented by Leica and then shared with Meyer before the Leica I Model C of 1930 to test the new LTM mount and its marketability. All appears to have turned out all right. Part of the fun of this subject is that more research is needed, so I am willing to volunteer for 6 months hard research at the Wetzlar Park 4 Seasons to make sure I get it right. It’s tough work, but someone has to do it.
That’s what everyone says, but one Italian expert begs to differ!
By Jason Schneider
Like most Leicaphiles I’d always assumed, based on the words of experts and historians, that Leitz had originated the 39mm Leica screw mount, aka M39 or LTM, back in 1930, first installed it on the early Leica I (Model C) in non-standardized form, and then standardized it on later Model Cs by adopting a uniform flange focal distance of 28.8mm. The Leica screw mount allowed lens full lens interchangeability among screw-mount Leicas from the standardized Leica I, Model C all the way up to the Leica IIIg of 1957-1960, the last of the screw mount Leicas.
But then I ran across Leica the First 60 Years by Gianni Rogliatti, in which the author states, on page 42: “As early as 1928 the Leica I had an ‘interchangeable’ lens. This was a conversion by Meyer who fitted one of their own f/1.5 lenses by means of a screw mount. As far as can be determined they originated the Leica screw mount. These cameras were advertised from 1928.” Indeed, a picture of a Leica I (Model C) with a 50mm f/1.5 Meyer Kino-Plasmat nicely mounted on it does appear on page 43 of the book, along with an ad by Meyer’s British Distributor A.O. Roth quoting a princely price of 39 Pounds Sterling for the (unnamed) Leica camera, f/1.5 lens, and 3 spools of film (presumably pre-loaded Leica cassettes).
Cover of G. Rogliatti's excellent volume on the first 60 years of Leica.
Leitz’s fastest 50mm Leica lens in 1928 was the not so fast 50mm f/3.5 Elmar! The Meyer 50mm f/1.5 was not just among the first interchangeable lenses for the new Leica (even if not rangefinder coupled since the Leica of that time had no built in rangefinder), it was amazingly fast for 1928. Indeed, the F1.5 Meyer Kino-Plasmat essentially invented Leica superspeed buy it off the shelf low light photography!
Copy of page 42 of Rogliatti's book. Note caption to image and last paragraph of text suggesting that Meyer devised the Leica screw mount.
The Meyer Kino-Plasmat lens, as its name suggests, was originally designed for cinematography, which in most cases meant the 24 x 18mm 35mm cine format, and that raises the questions of if and how well any of these lenses would cover the Leica’s 24 x 36mm format. However, it was by far the fastest super-speed lens of its day and even the films of the day were very slow (ISO 100 equivalent when pushed), so the motivation to mount one on a Leica would have been quite high in any case. Both the nickel-plated Meyer Kino-Plasmat pictured on page 43 and the larger 4-inch (?) one shown next to the lens-less Leica I (Model A) on page 42, bear the name of P. Rudolph. Paul Rudolph (1858-1935), one of the greatest lens designers at Carl Zeiss, was responsible for such legendary lenses as the Zeiss Anastigmat of 1889 (later sold as the Protar), the Planar, and the Tessar (1902). He was hired by Meyer in 1920, where he turned out the highly color corrected Plasmat, and the Kino-Plasmats, the fastest lenses of the mid ‘20s.
Detail image on p/ 42 of Rogliatti's book showing coarse 34mm diameter thread on Leica I (Model A) camera and on 50mm f/3.5 Elmar at right.
The Leica mount legend vs. revisionist history
If the time-honored creation story of the venerable Leica screw mount really turns out to be a myth, it would certainly be ironic, iconoclastic, and wryly amusing to those who scoff at the Leica mystique and cause consternation among Leica fanatics. However, before we can assess the veracity of the claims made my Rogliatti and others that the Hugo Meyer lens company may have invented the Leica screw thread mount that was then presumably “appropriated” by Leitz without any acknowledgement, let’s review the official narrative that has come down to us:
The humble screw mount that Leitz first installed on the non-standardized Leica I (Model C) in 1930 was a simple idea that ultimately transformed the Leica into what many consider to be the world’s first 35mm photographic system. The M39 mount, often called LTM (an acronym for Leica Threaded Mount), or simply Leica Screw Mount, is 39mm in diameter, and has a Whitworth thread of 26 turns per inch (tpi), which works out to a pitch of 0.977 mm, just shy of 1mm. Why Whitworth, rather than, say, metric? Because E. Leitz Wetzlar was a major microscope manufacturer, and the Whitworth system was the industry standard established by the Royal Microscopical Society (RMS) of England. Leitz was already using it for its microscope objectives, so the factory tooling was already set up to produce the Whitworth thread form. True LTM lenses also have a flange focal distance of 28.8mm, but that wasn’t standardized on early Leica I, (Model C) cameras produced prior to December 1930, known as “non-standardized Cs.”
1928 ad by A.O. Roth of London, the UK Meyer lens distributor, showing a fast Meyer lens on what looks liker an early Leica I (Model C).
The first screw mount Leica
The collapsible lenses permanently affixed to the original Leica I (Model A) and the Compur shutter Leica I (Model B) were problematic for Leica photographers who wanted greater optical flexibility. In characteristic fashion Leitz addressed it in the simplest, most direct way possible—they simply installed the M39 mount on what was essentially a Leica I (Model A), creating the Leica I (Model C), Leica Code name LENEU. This allowed you to mount a 3.5cm f/3.5 Elmar, a 5 cm f/3.5cm Elmar, or a 9cm f/4 Elmar on the camera body—but there was an important catch. Since these cameras were literally handmade, with slight variations in lens mount-to-film-plane distance and in the physical placement of the mount itself, each interchangeable lens had to be calibrated to a specific camera body. To ensure a proper match, the earliest iterations of these interchangeable Leitz lenses had the last three digits of the Leica camera body serial number engraved on the lens barrel. A total of 2,307 of these non-standardized Leica I (Model C) cameras were produced in 1930 and 1931, all now virtual museum pieces.
Early Leitz New York ad for the Leica I (Model C) extolling the virtues of its trio of interchangeable 35mm, 50mm, and 90mm lenses.
The issue of full lens interchangeability was resolved in the latter part of 1930 with the introduction of the standardized mount. The distance from the front of the lens mount to the film plane was fixed at 28.8mm, and it remained the same for all screw mount Leicas up until the very last Leica IIIg that rolled off the production line 30 years later in 1960. The standardized mount meant that any Leitz screw mount lenses could be used on any screw mount Leica without individual calibration, a simple spec that, combined with the ingenious rangefinder coupling system that debuted in the Leica II (Model D) of 1932, enabled the little Leica to become the dominant 35mm rangefinder system of the 20[SUP]th[/SUP] century. The first “standardized” Leica I (Model C) bore Serial No. 60501 and all subsequent Model Cs were standardized. Early standardized Leicas have an identifying “O” engraved on the top of the lens mount, and a total of 7,231 standardized Leica I Model C cameras were made.
In 1933 Leitz brought out the Leica Model E, widely known as the Leica Standard, all with standardized lens flanges. The only operational difference between a standardized Model C and the later Model E is that the latter has a smaller diameter rewind knob that extends to make rewinding easier.The M39 lens mount endured in its original form over an evolving succession of literally dozens of I- II-, and III-series Leicas from the ‘30s through the ‘50s, even in the face of a succession of ingenious bayonet mounts introduced by competitors including Contax, Exakta, and Nikon. The LTM mount was slower of course, but it was durable, straightforward, and it worked.
To get back to Mr. Rogliatti, his book, and his contentions regarding the origins of the M39 screw mount, it’s important to examine both his wording and the images in his book with great care before coming to conclusions. Gianni Rogliatti, who passed away in 2012 was an acclaimed automotive journalist, a close friend of Enzo Ferrari, had a warm relationship with the Leitz family, and wrote 3 highly respected books on Leicas including the volume cited. Here are his own words regarding the f/1.5 Meyer lenses fitted to Leica cameras prior to 1930:
“As early as 1928 the LeicaI had an “interchangeable” lens. This was a conversion by Meyer who fitted one of their own f/1.5 lenses by means of a screw mount. As far as can be determined they originated the LEICA screw mount.” Now for starters, the expression “as far as can be determined” is classic journalistic CYA that has essentially the same meaning as “to the best of my knowledge” or “as far as anyone knows.” Rogliatti is a conscientious journalist who’s giving his opinion but hedging his bets. His statement is fascinating but hardly dispositive.
Now let’s turn to the pictures in his book. The photo on page 42 shows a Leica I (Model A) identifiable by its “hockey stick” infinity catch, with its lens removed. To the right side of it is a collapsible 50mm f/3.5 Elmar and to the left of the camera is an unspecified Meyer Kino-Plasmat lens. If you look closely, you can see that both the mount on the camera body (which retains its footage scale) and the screw mount at the bottom of the Elmar,both have coarse threads that don’t look like LTM threads, which are much finer. Also, if you measure the diameter of the mount on the camera and correlate it with the known dimensions of the Leica A body, it works out to about 34mm, much narrower than the 39mm diameter of LTM mount. The unspecified Meyer lens can presumably also screw into the Leica A pictured, but its male screw mount is hard to see.
What’s going on here? If you remove the set screw on the mount of the Leica A you can unscrew and remove the entire “non-interchangeable” 50mm f/3.5 Elmar, revealing a coarse thread measuring about 34mm in diameter. This is the fixed part of the lens’s focusing helical, the moving part being the original threads on the end of the lens that screw in and out as you focus. But if you install a secondary single focusing helical (the kind in which the entre lens turns) on the lens itself you can use the original fixed part of the focusing helical attached to the camera as a de facto threaded lens mount! That’s exactly what’s been done here, and since the Meyer lens pictured also has its own built-in focusing helical all you’d have to do to mount it on the camera is add a coarsely threaded 34mm male screw thread at the rear and screw it directly into the Leica A. This would have been a much easier solution for Mayer, or anyone selling Meyer lenses, than engineering a new mount and modifying the camera. And once Leica came out with the standardized Model C in 1930, Meyer could simply make lenses in 39mm Leica screw mount, which they did in profusion throughout the ‘30s. Significantly, both the Leica display picture and the A.O Roth adof 1928 on page 43 show Meyer lenses fitted to Leica C cameras which would have had standardized or non-standardized 39mm LTM mounts.
As a clincher, even if Meyer had decided to make its own mount and install it on the Leica A it’s highly unlikely that they would have chosen a 26 tpi (threads-per-inch) Whitworth thread that only a microscope maker could love—they probably would have gone metric and made it 39 x 1mm rather than 39 x 0.977. And if Leitz had simply appropriated Meyer’s mount as their own without so much as a by your leave, they probably would have raised a stink.
Despite the weight of all this logical analysis I concede that it’s theoretically possible that Meyer could have pulled this off. After all even Marc Small, author of the authoritative Non-Leitz LEICA Thread-Mount Lenses has stated, “The noted British camera concern of A.O. Roth offered non-standardized Leica A and C bodies as early as 1927 fitted to take interchangeable Meyer 50mm f/1.5 Kino-Plasmat lenses.”
Whether this means that the Leica A bodies were modified with Meyer-designed LTM mounts depends on what you mean by “fitted,” but in my arrogant opinion the Meyer lenses in question were modified to fit the Leica A’s de facto threaded mount, not the other way around, and that by the time the Leica C rolled around it already had a Leica screw mount, complete with those Whitworth threads.
Or maybe not. According to the experts at LeicaShop Vienna the LTM mount was invented by Leica and then shared with Meyer before the Leica I Model C of 1930 to test the new LTM mount and its marketability. All appears to have turned out all right. Part of the fun of this subject is that more research is needed, so I am willing to volunteer for 6 months hard research at the Wetzlar Park 4 Seasons to make sure I get it right. It’s tough work, but someone has to do it.
