Carl Zeiss Jena
In the winter of 1946/47 Carl Zeiss Jena was facing a real disaster. The company was already shattered by the destruction of the plant due to the bombardments during the later years of the war followed by the “we-take-the-brain-strategy” of the US Army when they invaded Thuringia in spring 1945. The troops immediately occupied the Zeiss factory in Jena and took possession of construction blue prints, prototypes and the head of the scientific personnel. But now, almost two years later and after most of the buildings and facilities had already been reconstructed, the Soviet Army came to enforce their dismantling programme. They removed most of the machinery and transported it to Krasnogorsk and other places where they planned to establish a new optical industry. But what turned out to be the biggest burden was that the Soviets also took the rest of the scientists and many skilled craftsmen with them to start up their production in Russia and train their workers. Now the company was finally paying the price for its enmeshment with Hitler’s regime and his war crimes.
The Biometar as a replacement for the renowned Tessar
Despite this rather cheerless situation the people in Jena went on. The department for photographic objectives (“Abteilung Photo”) got a new head: Dr. Harry Zöllner. Trained in the company of Voigtländer in Braunschweig and just 35 years of age he was one of the youngest and at the same time one of the most experienced lens-designers available in Germany. Having perceived the enormous step forward the procedure of lens construction took due to the advancements of glass technology during the war, Zöllner began to rework most of the optical computations of existing constructions using these new sorts of glass; the most famous example being the Tessar 2.8/50 mm with the date of completion 29th of October 1947.
But the photo-optical department under Zöllner soon began to work on entirely new constructions. One target was to overcome obvious limits of correction that prevented the Tessars 2.8/50 and 2.8/80 from becoming absolute primes. Particularly lenses with a high opening (“speed”) suffer from Gaussian aberrations (“Gaußfehler”, refering to C. F. Gauß) that become most intractable and persistent. These Gaussian aberrations are caused by the chromatic dispersion of the light when it passes through optical glass. This dispersion of light into its spectral colours is affecting the spherical aberration of optical lenses in a way that this aberration tends to vary with the wavelength of the light. Similar effects arise concerning the coma of a lens leading to the very problematic transverse colour coma (“Farbquerkoma”). This transverse coma is causing a persistent softening of the image at high openings of the aperture. The above graphs show a direct comparison of this transverse colour coma of the Tessar 1:2.8 (fig. 1) and the Biometar 1:2.8 (fig. 2) included in the US patent of the Biometar.
This quite unusual comparison of two lens types in a patent can be seen as a direct result of Harry Zöllner having to enforce his Biometar against the prestigious Tessar. It is said that neither the heads of Zeiss Jena nor the officials of the communist party in East Germany wanted to give up the brand name and the international reputation of the Tessar. Zöllner had to fight almost a decade for his much better Biometar.
But the starting point of the Biometar was an era when the people in Jena wanted to leave behind war and dismantlement and start into a new age. And so did the former business partners of Zeiss Jena. One of the first camera makers in Germany that resumed production was Franke & Heidecke in Braunschweig. There was a huge demand of their Rolleiflex on the US market. Reinhold Heidecke had already worked on a prototype of a Rolleiflex with a taking lens 1:2.8 in 1934. This camera involved quite extensive construction work since this lens didn’t fit in the usual shutter type 00 forcing F & H to switch over to the larger Compur 0. Despite all the effort put into this prototype the Rolleiflex 2.8 did not go into serial production back then due to the fact that the image quality of the Tessar 2.8/80 mm (computation date 27th of February 1933) did not fully meet the requirements [cf. Prochnow, Rollei-Report, 1993, p. 190].
Biometar 80 mm version 1948
Beeing aware of the limited prospects of correction, Zöllner ceased working on the 80 mm Tessar design and changed over to a Gauss-type design. Carl Zeiss Jena was a pioneer of the Gauss-type. Paul Rudolph managed to make this original telescope lens – invented by Carl Friedrich Gauß in the early 1800s – suitable for photography purposes by correcting the astigmatism this type was prone to. On the other hand the Gauss-type promised a high potential for the correction of spherochromatic Gaussian aberrations. Willy Merté already used this potential to create his Biotar 1:1.4 in 1927. Harry Zöllner's idea was to use this potential not for creating a high aperture lens but to widely correct spherochromatic aberrations and the problematic transverse coma.
Zöllner therefore made a simplification of the Gauss-type by replacing the rear cemented group of the Biotar with a single, very thin meniscus of negative optical power. This single element was the centre point for the good correction of the Biometar, but it actually didn’t make the Biometar simpler. Manufacturing such a thin and highly curved meniscus was a huge challenge for an optical company by that time, since this type of element was very hard to centre-grind with the technical means of that era. Not every optical company was able to even manufacture them with the demanded precision. As a result the Biometar never could be a cheap lens.
Just made for a short period: Biometars for the Contax II (picture by Stefan Baumgartner)
As mentioned above for 35 mm photography Zöllner had developed the new Tessar 2.8/50 mm in 1947 and this lens was made for almost exactly 40 years without any change. So why did this Tessar-type not meet the requirements for a 6x6 Rolleiflex? There are two reasons. First the focal length is longer and most aberrations increase with the focal length. And second the usual 50 mm normal lens for a frame of 24x36 mm needs to cover a picture angle of only 45 or 46 degrees, whereas a standard lens for a 6x6 frame requires an angle which is almost 10 degrees larger. Spherochromatic aberrations reducing the image quality at the edge anyway will lead to an utterly unsatisfying sharpness when the angle of view is expanded even more. As a result Zöllner’s Biometar 2.8/80 mm accomplished in September 1948 (!) must be seen as an extraordinarily quick reaction on the demands of Zeiss Jena’s business partners. It was the best lens you could get for a Rolleiflex 2.8 by that time. But admittedly only 2000 pieces were made for the Rolleiflex. During 1949 two German states were formed, the Cold War began to overshadow the German economy and the foundation of a West-German Zeiss Company soon led into what literally has to be called enmity.
By losing the connection with Rollei the initial inducement the Biometar seemed to be gone, although the East-German camera industry did make 6x6 reflex cameras as well. However for the Primarflex II, the Master-Korelle and the upcoming Exakta 6x6 Zöllner's optical department computed a new Tessar 2.8/80 mm in July 1950. What didn’t seem good enough two years earlier seemed to be just good enough now. But paradoxically the production of the Biometar was NOT stopped. Zeiss Jena went on to put it in mounts for 35 mm reflex cameras like the Praktica, the Exakta, the Praktina and a 16 mm reflex movie camera called AK16. The production figures weren’t really large perhaps due to comparatively high costs, but steady. So the first lesson we’ve learned from the strange history of the Biometar: The version often seen as the one for 35 mm photography actually is the version created for the 6x6 Rolleiflex in 1948.
Since 1960 Zeiss Jena put this Biometar in modern mounts with fully automatic aperture mechanism for the Exakta bayonet, the Praktina IIA bayonet and the Praktica M42 thread. Unfortunately all these versions didn’t sell very well, since they were even more expensive than the very popular Sonnar 3.5/135 mm. As a result this type of Biometar went out of production during the second half of the 1960s.
Meanwhile the West-German companies Zeiss Oberkochen and Schneider Kreuznach had come out with similar 5-element Gauss-type variations for the Rolleiflex 2.8 with the Schneider version being shape-wise virtually identical with the Biometar.
It is hard to say why Carl Zeiss Jena didn’t apply for a patent for their Biometar in 1948 or 1949, especially because this new type was not just good as a standard lens for 6x6-cameras. At the Leipzig Spring Fair 1950 two new lenses were shown for the first time. One of them was the Biometar 2.8/35 mm; a wide angle design brought out as a replacement for the pre war Biogon 2.8/35 for the new Contax IIa from Stuttgart [cf. Die Fotografie, 4/1950, p. 89.]. The second was the Flektogon 2.8/35 mm – perhaps the first retrofocus wide angle for 35 mm reflex cameras ever made. What is interesting: This Flektogon 35 mm and a Flektogon 2.8/65 mm from the same year were based on a Biometar type as well. We must draw the conclusion that by that time the Biometar-type was seen as an all-round solution when high quaility was needed.
An all-round solution: The Biometar-type even allowed a good correction for viewing angles above 60 degrees – a bit like the West-German Planar. This Biometar 2.8/35 mm was made just for a short time in 1950 (less than 100 pieces), because the Soviet occupying forces transfered the whole production line of the Contax rangefinder cameras to the Ukraine. In the following years the East-German camera industry intirely committed itself to the single lens reflex type. As an reaction to this situation Harry Zöllner and Rudolf Solisch developed a wide angle lens with an enlarged back focal distance: The Flektogon 2.8/35 mm. This pioneer of the retrofocus lens was based on the Biometar-type as well. (picture by Stefan Baumgartner)
Biometar 80 mm version 1956
In 1956 the East German photo industry got a big boost. In September Kamerawerke Niedersedlitz brought a model of their new Praktisix to the Photokina in Köln. This 6x6 single lens reflex revitalised the medium format sector, since the Master-Korelle and the Primarflex were long gone and the Exakta 6x6 turned out as a false construction. When the Praktisix entered the market it was delivered with two Tessar-type standard lenses: The Zeiss Tessar 2.8/80 reworked in 1950 and a newly designed Primotar E 3.5/80 by Meyer Görlitz. It soon turned out that the optical department of Zeiss Jena was not at all satisfied with their Tessar. Notable rests of spherical aberration were responsible for a critical degree of focus shifting (“Blendendifferenz”) when stopped down. And since the Praktisix was the world’s first SLR camera providing exchangeable lenses with a fully automatic aperture mechanism – where the sharpness was always set at fully open aperture – there was focus shifting now practically at every shot. This was the moment when Harry Zöllner finally managed to convince Zeiss officials to drop the Tessar-design and switch over to the Biometar.
Interestingly Zeiss Jena did not resort to their existing Biometar 2.8/80 from 1948. In fact they used the opportunity to compute a completely new version getting rid of the limitations caused by the Rolleiflex design. Since the Praktisix was a SINGLE lens reflex camera the whole optical design did not need to be built as slenderly as possible like at the Rolleiflex, where two separate lenses had to be placed next to each other as close as possible. Free from such limitations, Zöllner’s optical department used the chance to enlarge the front element by a noteworthy degree in order increase illumination level in the corner of the image. This can easily be recognized by a direct confrontation of the front elements of the two Biometar versions.
Altough the computation of this new Biometar 2.8/80 mm for the Praktisix was finalised on the 5th of June 1956 this camera was equipped with the Tessar for more than two years until suddenly in spring 1959 Zeiss Jena switched over to Biometar. Since they both fit into identical mountings there is practically no outer cosmetic difference between the Tessar and the Biometar 80 mm for the Praktisix.
It happened to be the same spring 1959 when Zeiss Jena brought out the above already mentioned Biometars 80 mm for the 35 mm SLR cameras Praktina and Exakta with the latest fully automatic aperture mechanism (left, Praktina version). But note that these new ASB-lenses still contained the Biometar formula from 1948 originally intended for the Rolleiflex. On the right an early copy of the 80 mm Biometar for the Praktisix based on the 1956 formula.
Now finally in January 1957 Carl Zeiss Jena decided to apply for a patent in both German states (and more than two years later in the USA). The positive side of these patents for us today is that we can figure out what sorts of glass was used by Zeiss Jena. The second element for instance consists of high density crown glass type SSK10, which was conceived just a few years earlier by Werner Vogel and Wolfgang Heindorf in the Schott glassworks in Jena. The Biometar 2.8/80 from 1956 was a totally up to date standard lens by that time. Other manufacturers had to put in much more effort to make a lens such as good as the Biometar, resulting in six or even seven element designs. So in later years, when lenses were produced in a much modern way, the five element construction turned out to be very cost-effective as well. This might have been the reason why Zenza Bronica ordered some series of the Biometar for their cameras. Obviously there was a period in the 1970s when their usual lens supplier Nikon became too expensive. All we know is that Zeiss Jena made a batch of 3000 pieces in 1974, 5000 pieces in 1977 and another 560 pieces in 1979.
picture bei Ronald Stenzel
This Biometar turned out to be a very successful lens – in respect of the rather moderate selling figures of medium format cameras. Launched in 1959 it was made for almost exactly 30 years without any major changes – neither optically nor mechanically. Only a three layer multi coating was added in the mid 1970s. And made for such a long time for the Praktisix and the Pentacon Six, you can identify the full spectrum of cosmetic changes in the outer appearance of Zeiss Jena lenses during that period.
The Biometar 120 mm
In the course of the revision of the Biometar-type based upon high density glass in 1956 Zeiss Jena also computed a variation of this construction with a 50 % longer focal length. The Biometar 2.8/120 mm was intended both as a short telephoto for the 6x6 reflex camera Praktisix and as a medium telephoto for 35 mm reflex cameras. Of course it wasn’t a telephoto in the strict sense of this word, since it didn't feature a shortened back focal length like for instance at the Sonnar 3.5/135. As a result of that the 35 mm version of the Biometar 120 mm turned out to be quite bulky. But because of its salient potential to correct spherochromatic aberrations this version of the Biometar offered a very good quality as well – despite of the longer focal length. This is the reason why this lens turned out to be made for 30 years for the Praktisix and Pentacon Six without becoming outdated.
Compared to contemporary lenses offered by competing manufacturers by that time these 1956 Biometars show how Carl Zeiss Jena had fortuntalelly managed to catch up to the first class lens makers only ten years after the fatal dismantlement. Being able to bring out such market-driven products was a result of hard work not only put into the reconstruction of a certain plant, but also into the reconstruction of a whole country.
But in fact it was more than that. Summing up war time and post war period Germany had lost more than a decade of further development. It simply would not have been enough to reconstruct a company up to a level where they stopped in 1939. To keep pace with the international competition Carl Zeiss Jena started to embark on becoming one of the world’s pioneers of computer engineering.
Wilhelm Kämmerer, Herbert Kortum and Fritz Straube belonged to such a group of scientists and experts who were deported to the USSR in 1946, Their task was helping to build up the Soviet defence industry. After five years most of them were allowed to go back to Eastern-Germany. Only a small share of experts totally familiar with all of the technical secrets of their special field were sent for 18 months to the infamous “Island of the Forgetting”. Obviously the Soviet authorities expected this measure to be sufficient enough to ensure the scientists were losing touch to their field of expertise. The story is told that Kämmerer, Kortum and Straube used this compelled sojourn for long walks excogitating the principles of an optics computation machine.
At last having returned to Jena they started working on this optics computation machine OPREMA (“Optikrechenmaschine”) in May 1954. The project could be finished after only 7 ½ months (!) in early 1955. The whole computer was based on an electromechanical principle using 17,000 relays, 90,000 selenium rectifiers and 500 kilometres of cable. As a positive side effect of a construction based on polarised relays the power consumtion always remained less than an astonishingly low 40 watts.
Originally the programmable binary calculator OPREMA was conceived as a twin. Having no experience with such a huge machine the inventors build two identical computers which were supposed to work simultaneously to gain control over their reliability. After a period of time they realized this was not necessary so both systems were split to be used individually, resulting in doubling the processing power.
A performance of about 100...150 Hertz and a runtime for standard arithmetic operations between 120 and 1200 milliseconds might seem as a joke today, but compared to the technical standards of the 1950s this has to be seen as an immense progress. Not only that such computations required a much shorter time now, there also was no “operator fatigue” anymore. Bear in mind that despite of the availability of mechanical calculating machines up to this point computing an optical system was more or less manual work requesting an unimaginable level of concentration by those who had to do this job for hours. The OPREMA, however, never lost concentration.
Of course we are not yet in an era when computers became capable of optimizing a system automatically. But the OPREMA made it possible to compute even the slightest variations of optical paths in order to successively approximate to an optimum, including even complex skew line rays. Eberhard Dietzsch, the father of the later Flektogon 2.8/20 mm, states that an instant progress entailed by the OPREMA was a drastic reduction of “product defects”. Namely in order to verify the success of a computation of an optical system a pilot sample has to be made (“Versuchsmuster V”). Between 1948 an 1954 the first pass yield of these pilot samples was only 17%. By 1956, the first year the OPREMA reached its full capacity, the first pass yield abruptly went up to 70%. And our Biometars 2.8/80 and 2.8/120 were surely one of the first constructions to fully benefit from this new computation technology.
For the conclusion of this essay I just want to draw your attention to an aspect which seems to me just as important as the optical system itself: the mounting of the optical system. As I already pointed out the Praktisix of 1956 and the Praktina IIA from 1957 were the first single lens reflex cameras to feature exchangeable lenses with a fully automatic aperture mechanism. This means that the camera opens the aperture when cocked and closes it again shortly before the shutter begins to expose the picture. In order to ensure that the diaphragm is really closed to the working value when the exposure begins there was just a very small time span to adhere to while the mirror was flipping up. This is the reason why at the Biometars 80 und 120 mm the aperture mechanism had to be mounted in ball bearings.
These new requirements initiated by the progress of the camera technology led into the highly fruitful era of cooperation between the optical department of Zeiss Jena and the camera-manufacturing of the (later) Pentacon works in Dresden during the 1960s. This soon turned out to be the last time that mass-produced photo equipment Made in Germany was able to reach the status of an international top product.
Dietzsch, Eberhard: Die Entwicklungsgeschichte der Retrofokusobjektive vom Typ Flektogon; aus: Jenaer Jahrbuch zur Technik- und Industriegeschichte, volume 4, 2002, pp. 108 et seqq.
Hellmuth/Mühlfriedel: Carl Zeiss Jena 1945-1990, 2004, p. 175 et seq.
Kämmerer/Kortum: Oprema, die programmgesteuerte Zwillingsrechenanlage des VEB Carl Zeiss Jena; Feingerätetechnik 3/1955, pp. 103 et seqq.
Kerner, Immo: OPREMA und ZRA 1 - die Rechenmaschinen der Firma Carl Zeiss Jena, 2006.
Prochnow, Jürgen: Rollei-Report, 1993.
Zöllner, Harry: Das Foto-Objektiv in Praxis, Entwicklung und Fertigung, Jenaer Rundschau, 2/56, pp. 36 et seqq.
Marco Kröger spring 2021
last update: 26. July 2021
Yves Strobelt, Zwickau