The Tenax II: Zeiss' Action Camera from 1938: an essay with pictures

Zeiss Ikon Tenax II from 1938 with 4cm Sonnar

Tenax II [Zeiss Ikon Catalog number 580/27]

This essay is a summary of the material covered in depth in my book

The Tenax II: Zeiss Ikon's Precision Fast-action Camera 

see URL: <http://wesloderandnikon.blogspot.com/2017/07/the-tenax-ii-zeiss-ikons-precision-fast.html>

    The Zeiss-Ikon Tenax [II] of 1936-1941 was to be the director of camera design Hubert Nerwin’s masterpiece, combining high quality, precision and finish in a fast-operating and easily-handled, compact 35mm camera. Its images are in the rare 24mm X 24mm format. Most sources indicate an availability for only three years: 1938-1940. But production started in 1937 (E preface numbers), reached a high in 1938 (H numbers) with a continuing production into 1939 (I.H. and J numbers). A few, but not many, may have been assembled later. Zeiss Ikon first showed the camera at the Leipzig fair in April 1938. Total manufactured numbers may never be known. Simon Worsley has estimated 8500, with 2000 in 1937, 3000 for 1938, and another 3500 in 1939-1040.
    A few Tenax have “Made in Germany” engraved on their accessory shoes in front of their serial numbers. All of these have serial numbers in the E or H series dating them to 1937-1938. All appear to have been sold at a time when foreign exports were still important and possible. Most fall in the first 800 numbers of the H series and were intended for the North American market. These export cameras also have their lenses’ distance scales marked in feet rather than meters and sport 1/4 inch thread tripod sockets.
   Zeiss Ikon aimed its marketing toward a prosperous upper middle class customer looking for a high-quality, fast-action camera. It may have particularly appealed to women wishing to record family and social events.  At $207.00 American for the Sonnar-equipped version, the Tenax II was beyond the reach of most of the camera buying public. For those with deep pockets or professional needs, the more sophisticated Contax or Leica with their wide range of lenses and accessories must have seemed to be the better investment.
     Most of our knowledge of the Tenax comes from interviews with the late Hubert Nerwin, ebay and auction listings, the Thiele databases and the research done by Peter Dechert, Bernd K. Otto and, more recently, Larry Gubas.
   New ebay listings show up a couple of times a month. Tenax that start low sell, but so far the highest “sold” price I have found was for a Tenax in South Korea at $499.00. Tenax offered at ebay "start" prices over $500 seldom sell, despite repeated re-listings. Tenax with the more modest Tessar lens often sell for less than $400.00. Few of the auxiliary lenses have shown up and with prices over $800.00, they do not sell either. Auction prices cover a wide range. In the early 00s, high prices seemed to be the norm, but by 2009 the prices had dropped to close to ebay’s. Recent auction prices have been higher. The Westlicht Auction House seems to be the only place where the rare auxiliary lenses and accessories appear. By contrast, the relatively plentiful and unglamorous Nikon S with over 34,000 built, routinely sells for more than $400.00. The Tenax and its accessories may be collectors’ items, but not enough to send the prices up to the Leica and Nikon levels.

German Naval Sonnar lens for Tenax II.
Note the number on the rear mount.

       A number of variations have shown up. Both the German Navy (Kriegsmarine) and Luftwaffe used the Tenax. Surviving naval cameras and/or their lenses have an added “Mxxx” or "MFxxx" inventory number as well as regular serial numbers. The M stands for "Marine." No one can agree on what the "F" means. Luftwaffe Tenax seen have "Luftwaffe Eigentum" engraved on their accessory shoes.
    The Tenax body also was the basis for a closeup camera body used during the war that lacked the body’s viewfinder/rangefinder and shutter, but did have an over-sized advance and larger counter and a huge rewind crank. These were used for photographing X-rays and on microscopes—a purpose the square-framed camera was probably ideal for.

Start of autumn

Grammy reading to Charlotte, age 8 months.

Leaf on our driveway. Ektachrome ASA 100

    The Tenax came without flash synchronization, but this must have been a popular after-market addition. More than a dozen Tenax have appeared on ebay with added PC posts. Location of the synch posts include left front, right front low, left of accessory shoe on top and right of the accessory shoe on top. Some of the adaptations appear crude, others are so well finished they look like factory jobs.

Lens production is another question, with a few showing 1936 numbers and the balance falling in Zeiss number ranges for either 1937-1939. Early normal lenses are often mixed in with late cameras, so mounting on cameras must have been done long after the first lens was finished. Several web sites have claimed that more cameras were sold with Tessars than Sonnars as the normal lens, but Thiele’s numbers disagree.[As do sales and auction records. See the discussion of lens production below.]

Zeiss offered four lenses for the Tenax II. The normal options were either a 4cm f2.8 Tessar or a 4cm f2 Sonnar. A long-focus 7.5cm f4 Sonnar and a wide-angle 2.7cm f4.5 Orthometar completed the offerings. [For a description of the 7.5cm Sonnar go to 7.5cm Sonnar. For detailed information on the Orthometar go to 2.7cm orthometar.] It is curious that Zeiss did not attempt to offer a second telephoto lens in the 100-115mm range since the 135mm Sonnar was the most popular auxiliary lens for the Contax cameras. My tests indicate that regular lenses of 85mm or longer vignette—as longer lenses also do on the Robots. Zeiss did produce a few prototypes of other lens types but did not venture outside the 27–75mm range. The onset of the war may also have contributed to the end of the system’s lenses development.

Other accessories that were available included a contameter closeup set (Cat.#1339) that is almost exactly like the set for the Contax (#1343), lens hoods, filters (35.5mm screw-in or 37mm slip-on) and an adapter for using the normal lens on an enlarger. The two studs on either side of the finder window take a mask (#580/7) to narrow the view to the coverage of the 75mm Sonnar. Two kinds of finders for the accessory shoe have also been seen: 433/17 and 432/8.
For information on closeups check out my recent blog entry: Closeups with Tenax II

Tenax II with Contameter type 1339

Description and operation of a Tenax II (Serial number: H. 76652)

    The shape and finish of this mid-production Tenax is on par with a Contax II or III. The leather is of highest quality and the black paint and chrome well done. Most Tenax show wear on the advance handle and this camera is no exception. Zeiss cameras are notorious for their “Zeiss bumps,” bulges in the leather that are a result of the chemical reaction of the acid in leather to brass. This camera has a few bumps on its back, plus a small amount of verdigris around the base of the self-timer. This has caused the leather to lift and interferes with the self-timer’s function, although the timer does operate with a slight nudge.
    The back is completely removable, as is the takeup spool—which is the same as used in the Contax II, III and other Zeiss 35mm cameras of that period. The camera will take Zeiss reloadable magazines or standard 35mm cartridges. If one uses the Zeiss magazines, one can load magazine to magazine and save the bother of rewinding.

Sassafras in fall

Left to right: rewind, sync post, shoe, rewind button, frame counter with release.

    Loading the camera is not nearly as easy as the quick-load features found on SLRs made in the late 20th Century. You have to insert the tongue of the film into a slot of the takeup spool, then place both the cartridge and the spool into their pronged bays. Holding the camera with the top tilted down to avoid having the film fall out, you then place the back onto the camera and secure it by turning the two keys on the bottom. Wind-off two frames, take up the slack and check that the rewind is turning when you advance to the next frame and you are set to go. The frame counter resembles the shutter speed dial of the Contax II. It is marked for up to forty-nine exposures per roll. Turn the counter clockwise using the two nubs until you are at zero.
    Continuing with the top of the camera: The shutter release is inside the frame counter. It is threaded for an internal compur-style cable release. Note the set of red dots. They should line up with each other. If you set the shutter to B, press the release and while holding it down, rotate the release button clockwise, the shutter will lock open—sort of a “Time” setting. Rotating the release back to where the dots line up, and the shutter will close. The 35mm Nettax and Super Nettal use the same method of gaining a "time" setting. At least one Tenax offered on ebay claimed that its shutter was broken. A close examination of the pictures clearly showed that the button had been locked down as described above. If the lucky winner of the camera turned the button when he got his camera, he probably found that he now had a fixed shutter.
    To the left and rear is another button that releases the film sprocket drive to allow rewinding the film.
   In line with the lens is a standard accessory shoe. No provision for flash sync, although many of the Tenax had sync added, as has this one with a PC outlet to the left of the shoe. The rewind is in the usual position, but in this case consists of two lift-up semi-rings. These appear to have been taken directly from the film advance on the Super Ikonta B. Either one can be raised to return the film to its cassette.
    The front of the camera consists of the lens mount surrounded by an array of four levers. The large lever to the right of the lens mount advances the film and cocks the shutter with one smooth, downward swing. Note that you do have to make sure that you press the lever all the way down or else it will not return to its set position. For 1938, this had to have been one of the fastest ways to advance film manually. Zeiss advertised that one could achieve an exposure or more per second. In practice, this is unrealistic. Every time one pushes down on the lever, the camera jerks unless anchored to a steady tripod. Still, it is easy to use and almost unique. The only other cameras to offer such an advance were the Tenax I of 1939, the Adox, and  Konica 35s from the mid-Fifties.

Front of Tenax II with Sonnar lens.

    At the bottom of the lens is the focus lever. Rotating this counter-clockwise approximately 30 degrees carries the lens from infinity to one meter. The lever surface has depth-of-field marks for f5.6 and f11—a nice touch. In use, the lens rangefinder patch shifts so quickly that it is easy to pass the point where the images coincide. One has to move the lever slowly. This is quite a contrast to the Leicas with their 200 degree rotation or the Contaxes with their 274 degree turning. The lens itself is a 40mm f2 Sonnar manufactured by Carl Zeiss Jena (six elements in three groups) and it is coated.
    The next lever sets the shutter speed. The lever projects from a flange that is also the face of the lens mount. Since a mounted lens covers that flange, the shutter speed settings are engraved on the front of each lens. Speeds range from one second up to 1/400th of a second plus B using a Compur Rapid shutter adapted from the ones used on medium-format cameras. This shutter lies at the heart of the Tenax’s design.
   Leitz had designed and patented what was and is one of the best cloth focal-plane shutters for 35mm cameras. It combined simplicity with reliability. It also gave lens designers full freedom to use a wide range of lens formulæ, including ones with deeply-set elements. The vertical-running shutter found on the Contax, Super Nettal and Nettax was Zeiss’ attempt to build something different that offered more features and yet avoided any infringement of Leitz’s patents. But it was an expensive, complicated design.
And it competed against the obvious alternative. The Munich-based firm of Deckel—a company partly owned by Zeiss— has been building reliable leaf shutters since the the turn-of-century. Many 35mm cameras used Deckel-built Compur inter-lens shutters in their cameras. But interlens shutters limited the lens options. Full interchangeability of lenses was not possible if one wanted to connect the film advance to the shutter cocking. Often these cameras offered only front-cell focusing.

       What Nerwin did was place a Compur shutter behind the lens mount. This allowed full linkage of advance and cocking and full interchangeability of lenses. But this novel solution was not without its drawbacks. The shutter used had to be a #0—larger than the #00 interlens shutters used in other 35mm cameras. This in turn meant that the fastest shutter speed could be only 1/400th of a second instead of 1/500th as in the Kodak Retina cameras. It also forced Nerwin to reduce the frame size to 24mm X 24mm instead of the standard 24mm X 36mm in order for the shutter opening to cover the full film frame. Apparently Nerwin did not mind this reduction. A shorter frame size allowed a snappier film advance and a more compact camera with smaller lenses.
    A behind-the-lens leaf shutter may have given the Tenax full lens interchangeability, but this did not mean that any lens could be used. The Tenax uses a simple bayonet, but its four lenses all feature deep set back elements that seat at least somewhat into the camera body. This allowed the exit pupil’s light to clear the shutter and give full coverage to the 24 X 24 format. But any lens that does not seat into the mount will almost certainly vignette due to the small opening of the leaf shutter (slightly over 24mm). But optics that have really deep back elements, such as the 35mm Biogon would not work either. Robot cameras have a similar problem.

The four lenses offered for the Tenax II: 2.7cm Orthometar, 4cm Tessar, 7.5cm Sonnar and 4cm Sonnar

       The accessory lenses may reflect this exit pupil restriction in their modest apertures, but, unlike the Nettax and many of Zeiss’ folding cameras, Zeiss did not scrimp on optical quality with the Tenax optics. The 7.5cm Lens is a Sonnar as good as the 8.5cm and 13.5cm Sonnars for the Contax. Unlike the Tessar based 35mm Elmar and the f3.5 W-Nikkor, the 2.7cm Orthometar is a six-element design derived from an aerial camera lens with little or no rectilinear distortion. Its tiny inner elements must have required considerable care to shape and grind and that difficulty was reflected in a price of $132.00 (well over $2200 in today’s dollars). The 7.5cm Sonnar cost $120.00

    At the top of the lens mount and next to the rangefinder window is the lens release lever. Depress this and rotate the lens clockwise for about 30 degrees and the lens comes off. The bayonet has three prongs. Because of the rangefinder module, the lens offers double-helical, non-rotating focusing—a nice and rare feature in the 1930s. Note that you should move the shutter speed setting to 1/50th of a second or slower before dismounting a lens, otherwise the lens will not rotate fully to its removal position.
       The Rangefinder mechanism in the early Leicas uses a pivoting prism behind the right-hand rangefinder window linked to a spring-loaded arm that moves against a shaped cam that projects out of the rear of a lens. It is a simple, easily adjusted mechanism—and was patented by Leitz. Zeiss first attempted to get around this problem by using a pivoting mirror. This proved to be unreliable.
    By the time the Contax II came out, Zeiss was using a different method of focusing a rangefinder, one that would find its way into almost all of Zeiss’ RF cameras. This was the rotating wedge lens [the Contax II and III use a similar sliding wedge]. In this mechanism, two wedge-shaped lenses are mounted back-to-back. As the picture lens moves, the wedge lenses rotate relative to each other to move the rangefinder image. On the Tenax II, the rotating wedges are mounted on an external arm and geared to the lens helical. The beauty of this system is that the camera itself contains no moving parts for its rangefinder. The helical drives the wedges, one which rotates clockwise, the other counter-clockwise. The drawback is an arm extending out of each lens that brings these lenses in front of the rangefinder window in the camera body.
        The Tenax’s rangefinder/viewfinder is one of the best found on any pre-war 35mm camera. The view is life size and the rangefinder spot a warm orange, contrasty and quite easy to see. The eyepiece however is small and viewing the complete frame may be difficult.
    The final item on the front of the camera is the self timer, mounted horizontally and labeled “Compur Rapid.” To use it, you must first tension the shutter, then turn the timer lever up. Pressing the shutter release will then start the timer. Its placement next to where the focusing finger goes can be a nuisance.
    The name “Tenax” is engraved on the right, lower corner of the front escutcheon. To its right, the Zeiss-Ikon logo is stamped into the leather. There is no indication that this is the Tenax II, a term used by Zeiss Ikon in its advertising after the introduction of the smaller, simpler and cheaper Tenax which Zeiss in advertising referred to as the "Tenax I." The Zeiss Ikon logo is also embossed in the back leather. The serial number appears on the accessory shoe and inside on the back next to the pressure plate. Export Tenax have “Made in Germany” engraved below the serial number on the accessory shoe.
           The lens on this particular Tenax is the more-expensive and better-quality 4cm (40mm) f2 Sonnar. Unlike most Tenax lenses, this one is coated, perhaps because it was intended for the military. The beauty ring indicates a “Carl Zeiss Jena” lens. Engraved on the back of the lens mount is “M188,” indicating a lens used by the German Navy. Filter size is 35.5mm screw-in, 37mm slip-on.
    The camera is a pleasure to handle and take pictures with. One wants to take it everywhere—which was Nerwin’s intention.

Several statements made on the Web that need refuting:

        The Tenax II was NOT Zeiss’ answer to the Robot cameras of 1934. Except for the square format, the two camera types share nothing in common. Nerwin denied that the Robot had anything to do with designing the Tenax. Robot cameras used a rotary shutter powered by a hand-wound spring motor. They required that the film be loaded into special cassettes and there was no provision for rewinding. They were marketed to industrial and professional users who needed a motorized camera for fast shooting or remote photography. Heinz Kilfitt designed the original Robot which Otto Berning patented and manufactured. Neither individual had anything to do with the design of the Tenax.

    The machinery, parts and plans for the Tenax II disappeared during the destruction of the old Ica Werk factory (along with all the equipment and plans for the Contax) during the fire bombing raids on Dresden in February 1945. Zeiss-Ikon had neither the interest or resources to revive the camera after the war. The facilities for making the Tenax I did survive the war and East German Zeiss manufactured and sold several versions of that camera well into the 1950s.

          The lenses for the Tenax II could require an essay by themselves. Using Thiele’s listings and dates, we might be able to follow the design process that led to the final four lenses Zeiss offered.
       The first Tenax lens was a 7.5cm f3.5 Tessar with one sample. This would be an interesting optic to examine and it must be unique. Date: July 1935—a time when the Tenax was still little more than drawings and words.
    August 1936, two 4cm f2 Sonnars were completed. Again, just samples of what was to be the  standard lens. By this date, the Tenax would have been in the final design stage.
    March 1937 sees a parade of various prototypes. Two 4cm f3.5 Tessars, two 3.5cm f2 Biotars, one 7.5cm f4 Sonnar.
    By April 1937, this prototyping appears to be over. The camera itself was now in production, and Zeiss Ikon needed the lenses. 1000 4cm Tessar f2.8 were built that month.
    In May 1937, 1000 4cm f2 Sonnar were built.
    In June 1937, another 1000 4cm f2.8 Tessar made it off the production line.
    A pause followed, but in August, Zeiss completed another 2000 4cm f2 Sonnar.
    Apparently that number filled the needs for the first camera production runs because the it was not until May 1938 that Zeiss finished another 3000 Sonnar. At least 610 more Sonnars were authorized as part of the same order that resulted in the first 6000, but 300 of those were not completed until August 1940 and the final 310 were finished in January 1941. This would indicate a total production of 6612 of the f2 4cm Sonnar.
    The Tessar work order that resulted in the first 2000 led to another 2000 by July 1938. A final orphan appears to have been built by April 1940. Total number of 4cm Tessars: 4001.

    In the meantime, the 7.5cm f4 Sonnars all came out as a result of a January 1938 work order but production ranged over several months. January saw 200 finished. That must have met initial demand for the next completion date is December 1938 when Zeiss made another 400. April 1939 saw another 150. October 1940 was to be the final run with 275, bringing the total number of 7.5cm Sonnars to 1026. Not too small a number, but 50 or more of these may have gone to Robot for their cameras. It would be typical for production of an accessory lens to lag behind camera production. Lens manufacturers had to wait until enough new cameras had sold for there to be a market for the accessory lenses.   
    Production of the 2.7cm f4.5 Orthometar may have started earlier than that of the 7.5cm Sonnar, but we have no start date and only one finish date. Three lots appeared to have been completed: 2 prototypes then 100 and 200. The middle lot shows an end date of October 1937. The other serial number range suggest a 1938 production. Total number: 302.
    6612 4cm Sonnars plus 4001 4cm Tessars would suggest a total camera production of approximately 10,600, but it is possible that Carl Zeiss simply made more 4cm lenses in anticipation of future sales, or they may have been intended for the Tenax that ended up as X-ray cameras.

Conclusion: The Tenax II combines an original and innovative design with fine optics and the best handling of any pre-war 35mm camera. This helps make it a collector’s item today, but, if you can work around the square format, it still can be an excellent shooter as well.

Copyright Michael W. Loder, 2013, 2014, 2016. 2017 All rights reserved.