Zeiss Sonnar - History Part 1

One aspect of the fascination of the Sonnar 5cm f/1.5 is it's history. There are few lenses that have such a long and eventful story.

Ludwig Bertele and the Invention of the Sonnar 5cm f/1.5

The Ernostar

At the end of 1919 a 19 years old optic calculator named Ludwig Jacob Bertele moved to Dresden to start his new job at the Ernemann-Werke AG. Before he had been working as an apprentice for Optische Werke Rodenstock. At that time Dresden was a vivid metropolis full of startups, innovations, arts and culture. With companies like Balda, Ernemann, ICA and Ihagee Dresden was the German center of camera manufacturing. Ernemann itself was one of the biggest manufacturers of motion picture cameras and projectors. It was one of the few German manufacturers that produced their own photographic lenses too. The Ernemann-Werke were a large manufacturing complex in the east of Dresden that still exists today.

Ernemann Tower in Dresden

Ernemann Building with Zeiss Ikon logo

Ludwig Jacob Bertele can be characterized as an ambitious perfectionist and a hard worker. Although he had left school with 16 years he immediately registered at the Technische Hochschule Dresden for the winter semester as listener after he moved to Dresden. He was interested in mathematics and optics. In his time working for Rodenstock he developed through practical experimenting a deep understanding of lens optics that exceeded by far the knowledge of most of his colleagues. Dr. August Klughardt that invited this young optic calculator to enter Ernemann would later describe him as a genius lens designer. At that time working as a lens calculator was a quite hard and monotonous work. Calculation even of simple optics for microscopes, binoculars or projection lenses required hundreds or thousands of calculations done with slide rule, logarithm and sinus table day by day. Despite his young age Ludwig Bertele was already an exceptional skilled lens designer. His intuition and knowledge of how optics work was challenged soon after he entered Ernemann.

In 1921 Emil Mechau finished a new system of film transport for cinematic film projectors for Leitz, the optical compensation / Optischer Ausgleich. As one of the largest manufacturers of projectors Ernemann started the development of a solution by their own. For this new kind of projector a very bright lens with very high sharpness was needed. The optical design department of Ernemann-Werke took over the development. The head of the department Dr. August Klughardt gave Bertele free hand in designing and calculating this new projection lens. Ludwig Bertele started immediately the work on this and opted for a wide opening and optimized optical correction. After reviewing the results of a first prototype it was Alexander Ernemann that suggested that this kind of lens could be used as a photographic lens too. In early 1922 Ludwig Bertele finished the very ambitious design of the Ernostar 10cm f/2, a photographic lens with an unseen wide opening and optical correction. The Ernemann-Werke developed a matching compact photographic camera for 4.5x6cm photographic plates (Mittelformat / medium format), the Ermanox camera, that was released in 1923/24. Although the Ermanox and Ernostar outperformed the competition by a leap only about 100 were sold. Again Alexander Ernemann choose the right direction and challenged Bertele to create a smaller lens for the compact Ermanox. Ludwig Bertele optimized the optical correction, reduced the focal length and improved the brightness of the lens again. In 1924 he finished the design of the compact Ernostar 8,5cm f/1,8.

It was those Ernostar 10cm f/2 and 8,5cm f/1,8 that are considered a milestone and sparked great public interest. The reason was that it allowed taking hand hold images indoors without flash light and tripod for the first time. New genres of photography where created because of the Ermanox and the Ernostar. Stage photography in theaters or court photography are such examples. The wide aperture of the Ernostar allowed for available light photography for the first time. The name Erich Salomon is closely connected with this camera. He can be considered as the first photo journalist and created a lot of famous images of political or public personalities of this time.

In a scientific article from 1925 Ludwig Bertele described how he achieved the brightness and optical correction of the Ernostar 8,5cm f/1,8. The design uses 6 lenses in 4 groups with a front group of 3 cemented lenses. Ludwig Bertele kept this cemented triplet idea in future Ernostar and Sonnar designs. His triplet consists of 2 collective lenses and one dispersive one. His lens design follows a similar principle. The 2 front elements have a strong collective power. The third element is a strong dispersive one. The fourth element is of collective power again. He combines a very strong light collecting front with a dispersive image forming back in the total design and in the triplet group. This is a concept that he used for the Sonnar again later. Unfortunately there was a misconception in the design of Ludwig Bertele's Ernostar design. He calculated a light loss of 9% of his 4 element design compared to 3 element designs and argued that this small loss would be barely noticeable. Through cementing 3 lenses into one group he was able to reduce the number of glass-air surfaces from 12 to 8. He did not see a way nor need to reduce the design to 3 elements. In 1926 August Klughardt proofed with practical testing that the light transmission of the Ernostar is in fact one stop lower than expected. Since no anti-reflection coating existed at this time the internal reflections and absorption reduced the light coming through the Ernostar lens by 52%. Bertele's misconception was that the transmission depends on the efficiency of the whole lens not their elements alone. This error became an incentive to create the Sonnar design later.

Already in 1923 it came to a break in the relationship between Ludwig Bertele and his patron Dr. Klughardt. Although barely involved in the development of the Ernostar Dr. Klughardt started to downplay the role of his employee and show the result as his own creation. Ludwig Bertele was so disappointed about this behavior that he quit his work for Ernemann-Werke end of 1923. He regretted this move very soon and talked with Alexander Ernemann. In Spring 1924 Ludwig Bertele became the new head of the optical design department of Ernemann-Werke AG. His office was in the new Ernemann-Tower that later was used as logo for VEB Pentacon.

Ludwig Bertele's work on the Ernostar spawned a lot of different Ernostar variations that where used for still photography cameras, motion picture cameras and cinema movie projectors. In chronological appearance this were

• Ernostar 10cm f/2 ( Ernemann / 45x60mm / Ermanox )
• Ernostar 5cm f/2 ( Ernemann / 35mm cine film / projectors )
• Ernostar 4,2cm f/2 ( Ernemann / 35mm cine film / Kino )
• Ernostar 14cm f/2 ( Ernemann / 65x90mm / Ermanox )
• Ernostar 12,5cm f/1,8 ( Ernemann / 65x90mm / Ermanox )
• Ernostar 11cm f/2,7 ( Ernemann / 65x90mm / Klapp )
• Ernostar 16,5cm f/1,8 ( Ernemann / 90x120mm / Ermanox )
• Ernostar 8,5cm f/1,8 ( Ernemann / 45x60mm / Ermanox )
• Ernostar 7,5cm f/2,7 ( Ernemann / 45x60mm / Miniatur-Klapp )
• Ernostar 3,5cm f/2 ( Ernemann / 35mm cine film / Kinette )
• Ernostar 15cm f/2,7 ( Ernemann / 90x120mm / Klapp-Reflex )
• Ernostar 22cm f/2,7 ( Ernemann / 130x180mm / Ermanox )
• Ernostar 10,5cm f/1,8 ( Ernemann / 45x60mm / Ermanox )
• Ernostar 18cm f/2,7 ( Ernemann / 90x120mm / Tropen-Klapp )
• Ernostar 4,2cm f/1,5 ( Ernemann / 22x32mm / prototype? )
• Ernostar 24cm f/1,8 ( Ernemann / 130x180mm / Ermanox )
• Ernostar 5,2cm f/2 ( Ernemann / 35mm cine film / projectors )
• Ernostar 5cm f/1,9 ( Zeiss / 35mm cine film / Kinamo )
• Ernostar 2,5cm f/1,4 ( Zeiss / 35mm cine film / prototype? )
• Ernostar 5cm f/1,4 ( Zeiss / 35mm film / Contax prototype )

This list might be incomplete or in wrong order. A lot of the documents where lost during WWII. But it is easy to see that Bertele was busy with creating new Ernostar designs and perfecting his creation.

The Sonnar

In September 1926 Carl Zeiss Jena founded the Zeiss Ikon AG in Dresden. The new company was a fusion of many German camera and projector manufacturers including ICA, Goertz, Contessa-Nettel and Ernemann-Werke. The Ernemann-Werke should continue producing motion picture cameras and projectors but from now on manufacturing of all needed lenses was done by Carl Zeiss Jena only. Alexander Ernemann fought for keeping a small optical design office for development of new projection lenses. That is how Zeiss Ikon (former Ernemann-Werke) in Dresden had their own independent optical design office with 6 opticians and Ludwig Bertele as head of the department. Through the fusion Ludwig Bertele found himself in a difficult position. Carl Zeiss Jena had a large optical department in Jena with names like Ernst Wandersleb and Willy Merté. All of them with academic degree. As a self-taught optical expert he was afraid that he would be treated second rate and refused to go to Jena. Thanks to Alexander Ernemann and Emanuel Goldberg Ludwig Bertele could stay in Dresden as employee of Zeiss Ikon AG.

Goldberg played a large role in keeping Bertele in Dresden. The former director of ICA became the head of Carl Zeiss Ikon after the merge and the driving force of the restructuring and technological realignment. He foresaw that Bertele's Ernostar design would advance his Kinamo and be used for the secretly planed 35mm rangefinder camera. He believed it would be best for Bertele and Zeiss Ikon to keep Bertele near the new camera design engineers of the camera and optical department in the former ICA building in Dresden Striesen. Goldberg achieved an agreement with Carl Zeiss Jena that all Zeiss Ikon / Bertele lens designs belong to Zeiss Ikon and those lenses where exclusively available with Zeiss Ikon cameras. Carl Zeiss Jena became a simple lens supplier only. Zeiss Ikon could use all of the photographic lenses offered by the Carl Zeiss Jena product catalog but Jena was not allowed to offer Zeiss Ikon lenses to other customers.

In early 1929 Ludwig Bertele took a time out of 3 month and went on a journey to the United States (USA). The reason for the journey is unknown. Maybe he was thinking about moving to the US and starting a new life. In the end Ludwig Bertele missed his previous life in Dresden too much and went back to his hometown. During his journey he came to the conclusion that it was possible to further reduce the Ernostar design to 3 elements. With a patent from the 14th of August 1929 of this new Sonnar idea he started again at Zeiss Ikon.

Bertele's new promising approach came at the right time. Leitz had released their revolutionary Leica I camera back in 1925. Since then more and more photographers all over the world were picking up the small Leitz rangefinder camera. Nobody at Zeiss had expected this success of this new rangefinder camera concept and the new (smaller) 35mm film format. Meanwhile camera sales for Zeiss Ikon cameras where dropping. Even the Ermanox camera suffered declining sales numbers. So Zeiss Ikon secretly started to create an own 35mm rangefinder camera that will surpass the Leica camera and win back customers. A new fast lens for this new unnamed 35mm film camera could help to turn the tides. Goldberg set a high bar for this new rangefinder camera. On the lens side he declared the goals of an interchangeable lens mount and a wide range of usable lenses ranging from wide lenses to tele lenses and from cheap to expensive. This put a lot of pressure to the optical departments in Jena and Dresden.

In Dresden Ludwig Bertele started to work on the improved Ernostar design now for the smaller 35mm film format. The basic idea that he followed was to replace the third and forth lens element of the Ernostar with a single lens group. By bringing the number of lens elements down from 4 to 3 the number of glass-air surfaces was reduced to 6. This step improved the brightness of the new lens by 25%. Since Bertele was working for Zeiss now he had access to new high quality Schott glass. He incorporated this kind of glass in the new rear lens element. On 8th April 1932 Ludwig Bertele finished the optical calculation of the Sonnar 5cm f/2. This photographic lens had 6 glass lenses in 3 groups. With only 6 glass-air surfaces the new lens held the dreaded light loss through reflections in check. At the same time the optical correction of the lens was excellent. Images were sharp and contrasty.

At this time the new Sonnar 5cm f/2 already was the fastest existing 35mm film standard lens for still photography. The fastest standard lens from Leitz was the Leitz Hektor 5cm f2,5. The release of the Contax I would happen in summer 1932 and production of the new improved Tessar 5cm f/3,5 and 5cm f/2,8 in the new Contax mount had already started in 1931. Bertele had finished the calculation of the Sonnar 13,5cm f/4 on 8th October 1931 and Jena was already producing this new spectacular tele lens. But Ludwig Bertele was convinced that he could improve the 5cm Sonnar even further. On 10th October 1932 he finished the optical calculation of the Sonnar 5cm f/1,5. This photographic lens had 7 glass lenses in 3 groups. The final design shares a lot of similarities with Bertele's Ernostar f/1,5 VERSUCH lens. The brilliant idea of Bertele for this design was to fill the air space between the two rear elements with a third lens and therefore create a single group. This fill-up lens should have similar properties like air. But by using a glass element Bertele had the advantage to control the behavior of light passing the rear group.

Bertele's new lens design with cemented triplets in 3 groups was given the name Sonnar. It is an artificial name. Inspired by the immense brightness of the lens the name is derived from the German word Sonne / sun. In fashion of the time the suffix -ar (like in Tessar, Biotar) was appended to show that this is a photographic lens. But neither the Sonnar 5cm f/2 nor the Sonnar 13,5cm f/4 were the very first finished Sonnar lens. This title belongs to the Sonnar 2,5cm f/1,4 for 35mm motion picture film cameras. Bertele finished this bright lens already on 18th June 1930 for Kinamo and Movikon cine cameras.

Initially Carl Zeiss Jena wanted to go with the Tessar lens as only 50mm standard lens for the new camera. Willy Merté had calculated an excellent Tessar 5cm f/3,5 design and managed to improve it to f/2.8 on 8th October 1931. But Emanuel Goldberg insisted that a brighter lens was required. He wanted to advance the optics of the new camera to a new level and was not asking for less than a new milestone. He was thinking of Bertele with his Ernostar. But Jena did not want to give up its role as sole creator of camera lenses so easy. As reaction to Bertele's 1922 Ernostar Willi Merté was experimenting on new bright f/1,4 Biotar calculations since 1927 in Jena. Since Bertele was going to finish his new Sonnar designs it came to a competition between the Jena Biotar and Dresden Sonnar within the Zeiss company. 1928 the Kinamo got a new Ernostar 5cm f/1,9 while the 1927 Biotar 4cm f/1,4 for the Kinamo was canceled after 270 copies. The Kinamo got the very first Sonnar 2,5cm f/1,4 but it was only produced for 2 years. In comparison the 35mm motion picture film Biotar 2,5cm f/1,4 was produced from 1928 to 1945. Willy Merté created a new Biotar 5cm f/1,4 for 35mm motion picture film already in 1929 and this one was produced for different cameras like Kinamo, Debrie or Robot until 1941. But the new Contax camera was matted to the Sonnar 5cm f/1,5 and 5cm f/2 only for the next 2 decades. The 1933 Biotar 4cm f/2 was produced for motion picture cameras until 1938. Than it was replaced by the 1937 Sonnar 4cm f/2. This shows that the Biotar was mostly used for the smaller motion picture format and for other cameras not from Zeiss Ikon. There were direct comparisons of Sonnar and Biotar and even Ernostar lenses in this time within Zeiss to determine which lens should be used. Zeiss Jena seemed very determined to proof that the Biotar was the better lens. Emanuel Goldberg got very mad when he learned that a row of subjects stood in a curve to mask the strong field curvature of the prototype Biotar while the test photos taken with the Sonnar lens appeared soft toward the edges because of the flatter field. Ludwig Bertele found some nice words about Merté's Biotar but saw the extremely strong chromatic aberrations visible on wide apertures as a limitation while his Sonnar was usable at all apertures. In the end production of the Contax Sonnar 5cm f/2 started on 11.05.1932 and for the Sonnar 5cm f/1,5 on 18.10.1932.

Contax I with Sonnar 5cm f/2 and 5cm f/1,5

The new 35mm film rangefinder camera from Zeiss Ikon AG was given the name Contax. It was indeed a camera with the potential to surpass the Leica camera. The Contax I was released in summer 1932 to the public. Developed in complete secrecy from the public it was not even shown at the previous trade fair in Leipzig. The print media slowly picked up the news of the new Zeiss camera and spread it throughout Germany and the rest of the world. At the start only a small set of lenses was available

• Tessar 5cm f/2,8
• Tessar 5cm f/3,5
• Triotar 8,5cm f/4
• Sonnar 13,5cm f/4

This should change very soon since Zeiss Jena and Ludwig Bertele worked with high pressure on increasing the lens catalog of the Contax camera. Bertele alone created a high number of new Sonnar lenses. Here is a list in chronological order:

• Sonnar 2,5cm f/1,4 ( 1930-06-18 / Kinamo )
• Sonnar 13,5cm f/4  ( 1931-10-08  / Contax )
• Sonnar 7,5cm f/4  ( 1931-12-14  / Kinamo )
• Sonnar 5cm f/2,8  ( 1931-12-14  / Kinamo )
• Sonnar 5cm f/2  ( 1932-04-08  / Contax )
• Sonnar 5cm f/1,5  ( 1932-10-10  / Contax )
• Sonnar 8,5cm f/2  ( 1933-04-24  / Contax )
• Sonnar 1cm f/2  ( 1934-10-04  / Movikon K8 )
• "Olympia" Sonnar 18cm f/2,8  ( 1936-02-12  / Contax )
• Biogon 3,5cm f/2,8  ( 1936-03-16  / Contax )
• Sonnar 4cm f/2  ( 1937-04-16  / Tenax II )
• Sonnar 30cm f/4  ( 1938-08-15  / Contax )
• Sonnar 25cm f/4 ( 1939-11-10 / FHK 6x9 )
• Sonnar 12cm f/1,5 ( 1939-11-28 / FHK )
• Sonnar 1,5cm f/1,4  ( 1941  / 8mm-projectors )

The Contax camera was not seen as a simple Leica copy. It was and is seen as more technical advanced than the Leica camera. But this technical advantage comes at a price. It is seen as more expensive and technical more complex camera that can fail more easily. The Contax lenses on the other side are seen as the best lenses available in the 1930ies and 1940ies. Especially the fast Sonnar lenses an re considered as the jewels of the Contax lens lineup and as the fundament of the raise of Zeiss as an international brand worldwide known today. The credit for this goes to Ludwig Bertele the father of the Sonnar lens. Carl Zeiss Jena was very quiet about this fact. They tried to leave his name out of the public and to come up with a Jena substitution. But they needed the Sonnar 5cm as selling point. Even if most of the customers could not afford it to buy a Contax with a Sonnar 5cm f/1,5 it was a lens generated interest and desire. Zeiss knew this well. In old promotion material the Contax ist mostly shown with a Sonnar 5cm f/2 or f/1,5. Other lenses are shown in the background but the Sonnar was clearly the selling point for the public.